Make project_id nullable

## What does this MR do?
Fixes the broken migration which is not in sync with `db/schema.rb`.

It's to solve https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/469.


See merge request !4701

Update migration_style_guide.md with new details

See merge request !4693

Hide the Todo button in the collapsed issuable sidebar.

## What does this MR do?

Fixes a bug where the "Add Todo" button was displayed in the collapsed sidebar.

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

This shouldn't remove any other elements from the collapsed sidebar.

## What are the relevant issue numbers?

None

## Screenshots (if relevant)

Before:

![Screen_Shot_2016-06-15_at_11.41.46_AM](/uploads/27a1ace58cf8c44ad96accd3d0b32f11/Screen_Shot_2016-06-15_at_11.41.46_AM.png)

After:

![Screen_Shot_2016-06-15_at_11.40.53_AM](/uploads/91a8585680fc482682d0efafdba4d599/Screen_Shot_2016-06-15_at_11.40.53_AM.png)

See merge request !4686

Fix long commit message scroll issue.

Fixes horizontal scrollbar for long commit description.

## Before
![before_](/uploads/d261e26044d8ab451bc7768b16316253/before_.png)

## After
![after](/uploads/f27227a77d25d80b797e3ffc916d1957/after.png)

See merge request !4643

Show categorised search queries in the search autocomplete

Fixes #5885 

It works in 3 categories, Dashboard, Groups and Project.

## Dashboard context
![for-dashboard](/uploads/3a59f6ec008a972495597c8f2691c385/for-dashboard.png)

## Group context
![for-group](/uploads/f7aa413d56330a1d9b2e5562f95badf7/for-group.png)

## Project context
![for-project](/uploads/dabe04cf8758a056cf7b03da001ffd91/for-project.png)


## Screencast
![category-search-dropdown](/uploads/4d9513dcd6ccb6e24adefdf65f9bc778/category-search-dropdown.gif)



See merge request !4499

# Conflicts:
#	app/assets/javascripts/lib/common_utils.js.coffee

Toggle whitespace button for compare page

## What does this MR do?

Adds whitespace button to compare branches page.

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

Ruby code.

## Why was this MR needed?

Compare branches UX

## What are the relevant issue numbers?

Closes #17881.

## Screenshots (if relevant)

![Screen_Shot_2016-06-09_at_18.39.48](/uploads/8995a7bc8bea7fa3ff19446ebe49fb88/Screen_Shot_2016-06-09_at_18.39.48.png)

## Does this MR meet the acceptance criteria?

- [x] [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
- [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 you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !4569

Update CHANGELOG-EE

[ci skip]

See merge request !468

Fix emoji block selector.

Fixes #18465 and #18577

See merge request !4604

[ci skip]

[ci skip]

[ci skip]

[ci skip]

[ci skip]

[ci skip]

Update CHANGELOG

[ci skip]

See merge request !4695

Revert "Merge branch '18047-event-item-links-dont-look-like-links' into 'master'"

## What does this MR do?

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

## Why was this MR needed?

## What are the relevant issue numbers?

## Screenshots (if relevant)

## 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)

See merge request !4692

[ci skip]

[skip]

[ci skip]

[ci skip]

[ci skip]

[ci skip]

This reverts merge request !4544

Fixed issue when assigning no weight

![weight](/uploads/a61ce995c86f4b7fde30389b2b5eee1a/weight.gif)

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/18374

See merge request !458

Replace raphael-rails with raphael.js and split it from the rest of the JS

## What does this MR do?

Removes raphael.js and its related libraries from the default JS bundle.

It also removes raphael-rails because the gem is unmaintained and – for whatever reason – didn't want to cooperate with the way I was trying to require it.

This brings the default (compressed and minified) application.js from 354KB after the d3 MR (!4394) down to 324KB.

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

That tests pass and that there aren't errors on any pages (especially the Network page).

## Why was this MR needed?

It's only used on the Network page and was using way too much bandwidth for just one page.

## What are the relevant issue numbers?

#14372 #13165 

Follow-up to !4394 and !4516.

cc: @jschatz1 

See merge request !4519

CE to EE master

See merge request !465

Updated '.event-item a' color

## What does this MR do?

Changes the color of `.event-item` links.

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

Did you want this restricted only to the activity page or anywhere showing `.event-item`'s?

## Why was this MR needed?

UX

## What are the relevant issue numbers?

Closes #18047.

## Screenshots (if relevant)

![Screen_Shot_2016-06-08_at_20.07.54](/uploads/9670fbeb6fac7a334a83e11ffc05148c/Screen_Shot_2016-06-08_at_20.07.54.png)

See merge request !4544

added hover state to top nav links

## What does this MR do?

Adds hover state to top nav links.

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

Ney.

## Why was this MR needed?

UX.

## What are the relevant issue numbers?

Closes #18301.

## Screenshots (if relevant)

![Screen_Shot_2016-06-07_at_23.23.45](/uploads/dac8ed99eca99fbcccbd98028e947ee1/Screen_Shot_2016-06-07_at_23.23.45.png)

See merge request !4521

Due date can be removed from milestones

## What does this MR do?

Adds a button to milestone form to allow user to remove due date 

## What are the relevant issue numbers?

Closes #15063 

## Screenshots (if relevant)

![Screen_Shot_2016-06-02_at_08.32.03](/uploads/8bd4446abde745dd5b1e140a887ec694/Screen_Shot_2016-06-02_at_08.32.03.png)

See merge request !4428

Add shortcut to copy file content hash link

## What does this MR do?

* Allows for multiple shortcut handlers to be initialised
* Adds `y` shortcut to file pages to copy permalink URL.

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

Ney.

## Why was this MR needed?

UX

## What are the relevant issue numbers?

Closes #14470.

## Screenshots (if relevant)

![y-shortcut](/uploads/b81feb26d8e0d7d4996c4afa29f385d7/y-shortcut.gif)

See merge request !4496

#17804 Pipeline download artifacts text

## What does this MR do?

Improves wording to the pipeline artifacts download dropdown items.

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

I couldn't test this very easily, any tips?

## Why was this MR needed?

UX.

## What are the relevant issue numbers?

Closes #17804.

## Screenshots (if relevant)

See merge request !4391

New issue shortcut doesnt work on some pages

## What does this MR do?

1. Slightly tidies dispatcher switch case by utilising 'fall through' cases.
2. Adds shortcuts to project pipelines, milestones, builds and forks pages

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

I have a feeling that these may have been missed out of the case statements on purpose?

## Why was this MR needed?

Possible UX issue highlighted in #17929.

## What are the relevant issue numbers?

Closes #17929.

Closes #12616. (dup)

Closes #18123. (dup)

Closes #13688. (dup)

## Screenshots (if relevant)

See merge request !4393