Fix MySQL compatibility in zero downtime migration helpers

## What does this MR do?

This MR fixes MySQL for zero downtime migration helpers introduced in https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/3860

Closes #17711

See merge request !4239

fix group members api doc: remove emial

"Email" is removed in ae564c97

See merge request !4232

Add health check feature documentation

for https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/3888

@virtuacreative @axil 

See merge request !4199

Fix docker registry integration

See merge request !4229

Add README for updating .gitignore templates

Add notes to make it clear that users should not file a MR against a specific file here.

See merge request !4227

fix user.name length in milestones participants tab

Spelling mistake of "length"

See merge request !4206

Fix fork counter ui bug for safari

## What does this MR do?

Fixes UI bug on safari when fork button has blue arrow

## Screenshots 

![Screenshot_2016-05-19_22.10.21](/uploads/d923d8fc6bc12ee8f7052390bd5d7c51/Screenshot_2016-05-19_22.10.21.png)![Screenshot_2016-05-19_22.09.38](/uploads/130eb8b4a09b2ba5b7c5a83fed543dbf/Screenshot_2016-05-19_22.09.38.png)

See merge request !4221

Issuable form due date

For some reason, this was never in the original merge request for due date?

![Screen_Shot_2016-04-22_at_21.49.44](/uploads/7d4e2b07f75a33009e3170fdb076a4bd/Screen_Shot_2016-04-22_at_21.49.44.png)

Closes #15516

See merge request !3895

Fixed issue with enter key selecting wrong option in dropdown

If you search for a label and press enter the dropdown will select the last element rather than the first. This is because the currentIndex is -1 rather than 0

![labels](/uploads/eb29924109947fd63fea32e21471f05a/labels.gif)

Closes #17630

See merge request !4210

Fixed issue with merge button color

![Screen_Shot_2016-05-19_at_12.51.35](/uploads/a2768908553961e88c5a8f0e1f343078/Screen_Shot_2016-05-19_at_12.51.35.png)

Closes #17644

See merge request !4211

Wrap "No groups found" message with a .nothing-here-block

The "No groups found" message's style is inconsistent with the other empty messages.

## Screenshots

### Empty groups
![Screen_Shot_2016-05-13_at_13.40.34](/uploads/1447c5f60cde7d50d6f8f07c41704e5c/Screen_Shot_2016-05-13_at_13.40.34.png)

### Empty projects
![Screen_Shot_2016-05-13_at_13.40.30](/uploads/c21ff093f3d6bdbafecf7b075fa33d3c/Screen_Shot_2016-05-13_at_13.40.30.png)

See merge request !4137

Allows MR authors to have the source branch removed when merging the MR


closes #13191 

The location of the checkbox might not be optimal so any feedback is welcome. Any other feedback too obviously.

Screenshot:
![Screenshot_2016-02-17_21.25.24](/uploads/a9c3eaafb39c6f5b4f0949a2278af6da/Screenshot_2016-02-17_21.25.24.png)

See merge request !2801

# Conflicts:
#	app/services/system_note_service.rb

current_user.confirmed_at.present? => current_user.confirmed?

fixes: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/3862/diffs#4f7b76b1197d6fb073f77957b3b7b70d921ed7e7_42_41

See merge request !4225

Implement special GitLab markdown reference for milestones

https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/3453 by @eReGeBe, with two additions:

- Move changelog item to 8.8
- Fix cross-project milestone ref with invalid project, like https://gitlab.com/gitlab-org/gitlab-ce/commit/f7348cd348ad8f4a18d74dd668283a4e236f5790 did for labels

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/13829

See merge request !3897

Fix group visibility level migration in case all visibility levels are restricted

fixes #14632 

See merge request !4107

Let users set notification levels in projects which they are not members

Fixes #9013 

See merge request !3986

Add .gitignore dropdown when creating a new .gitignore file
Signed-off-by: Alfredo Sumaran <alfredo@gitlab.com>

Fix Error 500 when attempting to retrieve project license when HEAD points to non-existent ref

Closes #17537

See merge request !4151

Use extended regexp flag for `git grep`-ing files

Closes #3055

See merge request !4203

A access token -> An access token

Update CE code to include some refactor done in EE to do with import url

This is simply updating the code to match EE and avoid further conflicts related to `import_data` and `import_url` changes made on EE only.

See merge request !4223

Updated the DB schema

This updates `db/schema.rb` which apparently wasn't fully updated in the recent merge requests.

See merge request !4222