- Tab between register and sign in forms
- Add individual input validation error messages
- Validate username
- Update many styles for all login-box forms

Enforce TrailingSemicolon and EmptyLineBetweenBlocks in scss-lint

## What does this MR do?
Enforces two new scss-lint rules
1.  TrailingSemicolon
2.  EmptyLineBetweenBlocks

## Are there points in the code the reviewer needs to double check?
Make sure I didn't break anything 😁 

## Why was this MR needed?
Improve our SCSS, Lessen the burden of catching these during the review process

## Screenshots (if relevant)
NOne

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- Tests
  - [x] All builds are passing
- [x] Conform by the [merge request performance guides](http://docs.gitlab.com/ce/development/merge_request_performance_guidelines.html)
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if it does - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

## What are the relevant issue numbers?
Closes #23319

See merge request !6903

Added subnav to all views bar issuable views

## What does this MR do?

Adds subnav to all views apart from issue and MR views. The full list is available in screenshots below.

It also adds some JS to the builds page to simply handle the repositioning of the fixed position sidebar with the addition of the subnav.

## Are there points in the code the reviewer needs to double check?

## Why was this MR needed?

~UX and apparently ~regression .

## What are the relevant issue numbers?

Closes #18844.

## Screenshots (if relevant)

### Label

#### Edit

![Screen_Shot_2016-08-24_at_23.45.25](/uploads/3e5ded9e60f0eccc37672ab0a1423bfb/Screen_Shot_2016-08-24_at_23.45.25.png)

#### New

![Screen_Shot_2016-08-24_at_23.45.13](/uploads/767c6e97c91a5ded904f5b495950f5a8/Screen_Shot_2016-08-24_at_23.45.13.png)

### Milestone

#### Edit

![Screen_Shot_2016-08-24_at_23.45.37](/uploads/27562162415a6ae403e7117df009b208/Screen_Shot_2016-08-24_at_23.45.37.png)

#### New

![Screen_Shot_2016-08-24_at_23.45.43](/uploads/43c655b0a2af9a8da335a2efc31cb2df/Screen_Shot_2016-08-24_at_23.45.43.png)

#### Show

![Screen_Shot_2016-08-24_at_23.45.53](/uploads/68c3e0788c81f5897c7db11bb2b02a4c/Screen_Shot_2016-08-24_at_23.45.53.png)

### Commit

#### Show

![Screen_Shot_2016-08-26_at_14.15.20](/uploads/9f96e0587e4866fa95e28c224a185844/Screen_Shot_2016-08-26_at_14.15.20.png)

#### Builds

![Screen_Shot_2016-08-26_at_15.28.46](/uploads/9f0d8ababc8362874a3e2b5d877c7668/Screen_Shot_2016-08-26_at_15.28.46.png)

### Blob

#### Blame

![Screen_Shot_2016-08-26_at_14.18.03](/uploads/2999f2cd304e3b9be6530a52407eca59/Screen_Shot_2016-08-26_at_14.18.03.png)

#### Edit

![Screen_Shot_2016-08-26_at_14.20.32](/uploads/bb7b00bbe835228a8ec8b371e9364cb8/Screen_Shot_2016-08-26_at_14.20.32.png)

### Pipelines

#### Show

![Screen_Shot_2016-08-26_at_15.44.30](/uploads/ee84c51597ab04a07a6c953704280e7b/Screen_Shot_2016-08-26_at_15.44.30.png)

#### Show build

![Screen_Shot_2016-08-26_at_15.45.55](/uploads/dd78ef3dc083186095cdc84f41c80b21/Screen_Shot_2016-08-26_at_15.45.55.png)

#### Edit Envrionment

![Screen_Shot_2016-08-26_at_15.48.33](/uploads/4e9340e11eedeaeddebb708f02db3598/Screen_Shot_2016-08-26_at_15.48.33.png)

## Does this MR meet the acceptance criteria?

- [ ] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [ ] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- [ ] API support added
- Tests
  - [ ] Added for this feature/bug
  - [ ] All builds are passing
- [ ] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [ ] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [ ] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)
Closes #18844

See merge request !5998

Improved specificity of toggleable file headers

## What does this MR do?

Improves the specificity of the diff file title toggle styling.

## Are there points in the code the reviewer needs to double check?

## Why was this MR needed?

Currently, any `.file-title` will have a pointer cursor and background colour change on hover. This should be only for diff files, except discussion diff files.

## Screenshots (if relevant)

![2016-10-14_13.57.12](/uploads/e8561bed378487b8d14d579ce31417d0/2016-10-14_13.57.12.gif)![2016-10-14_14.01.15](/uploads/e88858874377fa83aa5e632ec9e1a601/2016-10-14_14.01.15.gif)![2016-10-14_14.01.46](/uploads/8a773ee6bb29386f2dc022bb2ffaf474/2016-10-14_14.01.46.gif)

## Does this MR meet the acceptance criteria?

- [ ] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [ ] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- [ ] API support added
- Tests
  - [ ] Added for this feature/bug
  - [ ] All builds are passing
- [ ] Conform by the [merge request performance guides](http://docs.gitlab.com/ce/development/merge_request_performance_guidelines.html)
- [ ] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [ ] Branch has no merge conflicts with `master` (if it does - rebase it please)
- [ ] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

## What are the relevant issue numbers?


Closes #23147

See merge request !6887

Improve tabbing usability for sign in page

## What does this MR do?
Rearranged the html elements so that the `sign in` button gets tabbed first before the other elements and used CSS to rearrange the visual layout.

I did not use `tabindex` because it does not play well with screen readers and is not recommended from an accessibility standpoint.

## Are there points in the code the reviewer needs to double check?

*  Need to make sure that there aren't any side effects to my code change. `.new_user` seemed to be automatically added through `form_for()` and I'm not sure if there will be other cases where `.new_user` is used where there is no sign in page with forget your password.

## Why was this MR needed?
Improves the tabbing order

## Screenshots (if relevant)
None

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- Tests
  - [x] All builds are passing
- [x] Conform by the [merge request performance guides](http://docs.gitlab.com/ce/development/merge_request_performance_guidelines.html)
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if it does - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

## What are the relevant issue numbers?
Closes #23279

See merge request !6867

Resolve "Build/Pipeline/Environment List Inconsistency Row Height"

#### What does this MR do?
* Changes generic table class from `builds` to `ci-table`. It was getting confusing using `builds` for `builds`, `pipelines`, `environments`
* Sets height on builds rows for continuity

#### Are there points in the code the reviewer needs to double check?
Apparently you can't set `min-height` on any `table` elements but you _can_ set `height`. For some reason, even if the content within happens to start wrapping, the row height will grow instead of letting the content overlap. Which is a good thing. Just kind of weird.

#### Why was this MR needed?
Different row heights on builds depending on content

#### Screenshots (if relevant)
Before:   
![Screen_Shot_2016-10-10_at_4.49.58_PM](/uploads/a4edb584f95c670f9815a8e5b1d725ee/Screen_Shot_2016-10-10_at_4.49.58_PM.png)
After:   
![Screen_Shot_2016-10-10_at_4.32.03_PM](/uploads/488a84b4ed292fbbb0ea7e372c017ae0/Screen_Shot_2016-10-10_at_4.32.03_PM.png)
Before:   
![Screen_Shot_2016-10-10_at_4.44.23_PM](/uploads/3cbcbada89d1aeb1fea35ea9b851e370/Screen_Shot_2016-10-10_at_4.44.23_PM.png)
After:   
![Screen_Shot_2016-10-10_at_4.42.56_PM](/uploads/0cb573670f60c7fdf54fdb027c95639f/Screen_Shot_2016-10-10_at_4.42.56_PM.png)

## What are the relevant issue numbers?
Closes #23167

See merge request !6787

Merge request tabs stick when scrolling page

## What does this MR do?

When scrolling merge requests this sticks the tabs to below the navigation for easy access.

## Screenshots (if relevant)

![sticky](/uploads/372a9889c50e9f85fef475cbee110ec1/sticky.gif)

## What are the relevant issue numbers?

Closes #20548

See merge request !6382