Improve design of Pipeline view

## What does this MR do?

Improves current design of Pipelines view when there is multiple stages.
This makes the statuses clickable and makes the view more compact.

## Screenshots (if relevant)

![Screen_Shot_2016-05-21_at_01.20.40](/uploads/dd031b7af7005c7a61f3165fefa8b7c9/Screen_Shot_2016-05-21_at_01.20.40.png)

cc @DouweM @markpundsack @rspeicher @marin 

See merge request !4230

Fixed potential issue with 2 ci status polling events happening

Possible cause for double notifications was if the request was slow & then you changed page whilst this request was happening it would finish on another page & then launch another interval - this stops that issue.

Also passed in the CI status as an option value rather than waiting for the first ajax request to finish

See merge request !3869

[ci skip]

Fix concurrent request when updating build log in browser

If you have a slow internet connection the trace will not be updated correctly. We need to check if our request is the latest one.

Fixes: https://gitlab.com/gitlab-org/gitlab-ce/issues/17535

See merge request !4183

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

Update branch name from 8-7-stable to 8-8-stable

Fix inconsistency with the command listed above.

[ci skip]

See merge request !4274

Fix typo in link on monitoring help page

Closes #17809

[ci skip]

See merge request !4281

Fix backups if registry is disabled

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/17749

See merge request !4263

Fix builds page

Fixes #17736    
Fixes #17703 

- Move tags into column
- Put column headers back

<img src="/uploads/57609fd2d65c3b80f57b32cbbe316653/Screen_Shot_2016-05-23_at_10.20.37_AM.png" width="800px">    



See merge request !4249

Fix Error 500 in CI charts by gracefully handling commits with no durations

## What does this MR do?

In the CI charts, this MR reports the duration of a commit to 0 if it is `nil`.

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

Should we omit this commit from the chart or set it to some other value?

## Why was this MR needed?

We were getting an Error 500 here: https://gitlab.com/gitlab-org/gitlab-ce/graphs/master/ci

## What are the relevant issue numbers?

#17730 


See merge request !4245

Fix Error 500 when accessing application settings due to nil disabled OAuth sign-in sources

## What does this MR do?

When upgrading to GitLab 8.8, an admin would encounter an Error 500 due to a `nil` `disabled_oauth_sign_in_sources`. This MR ensures that the value will be a blank array if empty.

Closes #17564

See merge request !4242

Initial version of user documentation of container registry

cc @axil


See merge request !4244

Allow anonymous user to access pipelines

## What does this MR do?

It fixes an issue where the Pipelines is shown for the Anonymous users,
but they get 404 when clicked. Their session is then logged out.

Fixes #17717.

See merge request !4233

Added remove due date button

In the sidebar when there is a due date a link to remove due date becomes visible

![remove-due-date](/uploads/126baa61f5ec44ce503ce374d5331ba6/remove-due-date.gif)

Closes #17392

See merge request !4209

Docker container registry configuration docs.

Part of gitlab-org/omnibus-gitlab!764 and gitlab-org/gitlab-ce!4040

See merge request !4141

Allow anonymous user to access pipelines

## What does this MR do?

It fixes an issue where the Pipelines is shown for the Anonymous users,
but they get 404 when clicked. Their session is then logged out.

Fixes #17717.

See merge request !4233

[ci skip]

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 the CI login to Container Registry (the gitlab-ci-token user)

## What does this MR do?

This fixes `docker login` not succeeding when trying to do CI login: `gitlab-ci-token with $CI_BUILD_TOKEN`.

cc @marin

See merge request !4236

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

[ci skip]

# Conflicts:
#	app/services/system_note_service.rb

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

Closes #17537

See merge request !4151

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

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