Support for measuring Ruby blocks using GitLab performance monitoring

This adds support for measuring timings of arbitrary Ruby blocks.

Fixes #14710 

See merge request !3515

Expose user location in API

* Closes #14720 

See merge request !3558

Ensure empty recipients are rejected in BuildsEmailService

Fixes #14883.

See merge request !3543

Optimise .gitlab-ci.yml

Not sure who should I assign.



See merge request !3542

Signed-off-by: Rémy Coutable <remy@rymai.me>

Added bottom margin to CLI instructions

The CLI instructions block in the empty project page is missing a margin-bottom style property. I added it, you can review the only line I edited to add this.

This only fixes a UX bug (to me), related to the "Remove project" button that is not correctly padded. Now I believe that part look better :)

I attach screenshots.

### before
![Selezione_009](/uploads/f46b2a26c192a0b1994ff2f037f50e6c/Selezione_009.png)

### after
![Selezione_008](/uploads/33a9451bbe8bfd9abd300f9c6eb4005f/Selezione_008.png)

See merge request !3505

API: Ability to retrieve a single tag

* Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/14330

/cc @dblessing 

See merge request !3567

This allows measuring of timings of arbitrary Ruby blocks, this allows
for more fine grained performance monitoring. Custom values and tags can
also be attached to a block.

Add CI styling to all CI updates

Fixes #14942 

Correct styling for last commit:
![Screen_Shot_2016-04-05_at_2.17.54_PM](/uploads/8cbda0023eaf7a26b776f3da58050e1a/Screen_Shot_2016-04-05_at_2.17.54_PM.png)

See merge request !3554

Fix Error 500 after renaming a project path

Renaming the path of a project would result in an Error 500 due to `@repository` being memoized with the old path. An Error 500 would result:

```
Started GET "/testing2/test1" for 127.0.0.1 at 2016-04-04 12:42:30 +0000
Processing by ProjectsController#show as HTML
  Parameters: {"namespace_id"=>"testing2", "id"=>"test1"}
Completed 200 OK in 637ms (Views: 194.2ms | ActiveRecord: 111.8ms)
Started GET "/testing2/test1/edit" for 127.0.0.1 at 2016-04-04 12:42:33 +0000
Processing by ProjectsController#edit as HTML
  Parameters: {"namespace_id"=>"testing2", "id"=>"test1"}
Completed 200 OK in 594ms (Views: 183.8ms | ActiveRecord: 87.4ms)
Started PATCH "/testing2/test1" for 127.0.0.1 at 2016-04-04 12:42:41 +0000
Processing by ProjectsController#update as HTML
  Parameters: {"utf8"=>"✓", "authenticity_token"=>"[FILTERED]", "project"=>{"nam
e"=>"test123", "path"=>"test123"}, "namespace_id"=>"testing2", "id"=>"test1"}
Completed 500 Internal Server Error in 1852ms (ActiveRecord: 124.0ms)

ActionView::Template::Error (no repository for such path):
    2:   %legend
    3:     Builds:
    4:
    5:   - unless @repository.gitlab_ci_yml
    6:     .form-group
    7:       .col-sm-offset-2.col-sm-10
    8:         %p Builds need to be configured before you can begin using Contin
uous Integration.
  app/models/repository.rb:59:in `block in empty?'
  lib/repository_cache.rb:19:in `fetch'
  app/models/repository.rb:59:in `empty?'
  app/models/repository.rb:471:in `gitlab_ci_yml'
  app/views/projects/_builds_settings.html.haml:5:in `_app_views_projects__build
s_settings_html_haml__782034335636359229_73397600'
  app/views/projects/edit.html.haml:87:in `block in _app_views_projects_edit_htm
l_haml___2388082585934859365_47390860'
  app/views/projects/edit.html.haml:8:in `_app_views_projects_edit_html_haml___2
388082585934859365_47390860'
  app/controllers/projects_controller.rb:54:in `block (2 levels) in update'
  app/controllers/projects_controller.rb:43:in `update'
  lib/gitlab/middleware/go.rb:16:in `call'
```

Closes #14885

See merge request !3528

Premailer shouldn't remove script tags from our emails

Closes #14943.

See merge request !3552

[ci skip]

Closes #14943.

Fix data check in update issue response



See merge request !3548

Dropdown arrow support

When the dropdown is open, you can scroll through the list of items with the up & down arrow keys. When an item is focused, the enter triggers the click event for that row.

Closes #14455

See merge request !3385

Notes form design update

Part of #3401

See merge request !3442

Closes #14885

[ci skip]

Attribution where it is due.

Inspired by https://news.ycombinator.com/item?id=11431969

See merge request !3546

Upgrade bundler-audit from 0.4.0 to 0.5.0

Bundler Audit can now run the `check` command with an `—update` flag to update the Ruby CVE repository before checking. This removes the need for two separate commands in GitLab CI ([source](https://github.com/rubysec/bundler-audit#synopsis)).

See the Changelog for more information: https://github.com/rubysec/bundler-audit/blob/master/ChangeLog.md#050--2015-02-28

See merge request !3433

Check permissions when importing project members

Closes #14899

See merge request !3535

[ci skip]
Signed-off-by: Rémy Coutable <remy@rymai.me>

[ci skip]
Signed-off-by: Rémy Coutable <remy@rymai.me>

Fix LDAP link and codeblock indentation



See merge request !3538

[ci skip]

Update language after doing all other operations

See merge request !3533

Added CHANGELOG for build notifications

[ci skip]

See merge request !3537

[ci skip]

Add comments to the SCSS Lint config file [ci skip]

This MR also adds some previously missing linters.

See merge request !3500

When importing members, and user does not have permissions to read
members in a source project, do not leak information about source
project existence. Notifiy user that project has not been found instead.