Delete notes via API

Supports deleting issues, snippets, and merge requests via the API.

* Closes #14944
* Closes #14845 
* Closes #6060 

@zj I did not see that you assigned yourself in #6060. Hopefully, you did not start yet.

@rymai In #6060 this is targeted for 8.7 release. Could you review that and maybe this still lands in 8.7. 


See merge request !3557

API: Ability to retrieve a single tag

* Closes #14330

/cc @dblessing

See merge request !3577

Allow a project member to leave the projected through the API

Closes #7687 


See merge request !3613

Un-instrument Banzai::ReferenceExtractor

No changelog entry since this isn't really something new compared to 8.6, instead it adjusts something that was added for 8.7.

See merge request !3676

Instrumenting this class together with Gitlab::ReferenceExtractor causes
a StackError for some reason. Since Gitlab::ReferenceExtractor has most
of the interesting code we'll only instrument that class.

API: Add iid filter to milestones

This was documented in the API docs but it was never working because the iid filter was never applied to the milestones. The tests were working by accident because the were checking the first element, which was by accident the request element. 

* Closes https://github.com/gitlabhq/gitlabhq/issues/10122

See merge request !3588

API: Expose updated_at for notes

* Closes #7954

See merge request !3560

API: Expose open_issues_count, closed_issues_count, open_merge_requests_count on labels

Partly fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/13238

See merge request !3569

Fix milestone removal problem when editing issues

fixes #1752 

See merge request !3571

Instrument Banzai code

See merge request !3659

Fix scroll bars shown in Revert dialogue box


## What does this MR do?

Eliminate scroll bars shown in Revert dialogue box, see the screenshots.

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

N/A

## Why was this MR needed?

Ugly scroll bars are shown in Revert dialogue box.

## What are the relevant issue numbers?

N/A

## Screenshots

![Screen_Shot_2016-04-05_at_15.27.10](/uploads/428295858ada7cd2fcdf1e831c42f8ec/Screen_Shot_2016-04-05_at_15.27.10.png)



See merge request !3532

Go back to gitlab-workhorse 0.7.1

See merge request !3656

We found out that 0.7.2 breaks shallow `git clone`. GitLab 8.7 will
work fine with gitlab-workhorse 0.7.1 too.

Fixed issue with dashboard/issues not filtering by milestone

Closes #15128

See merge request !3650

Decrease threshold for ABC Size metric in Rubocop

To 55.

References #3444

See merge request !3598

Store block timings as transaction values

See merge request !3649

If the measure method uses Transaction.current directly the SQL
subscriber (Subscribers::ActiveRecord) will add timings of queries
triggered by DB cleaner.

Standardize the way we check for and display form errors

- Some views had a "Close" button. We've removed this, because we don't
  want users accidentally hiding the validation errors and not knowing
  what needs to be fixed.
- Some views used `li`, some used `p`, some used `span`. We've
  standardized on `li`.
- Some views only showed the first error. We've standardized on showing
  all of them.
- Some views added an `#error_explanation` div, which we've made
  standard.

See merge request !3531

First pass at a Code Review guide

Largely borrowed from thoughtbot's code review guide, so attribution is
included.

[ci skip]

See merge request !3639

Updated UI for new merge request

Closes #2540 

![Screen_Shot_2016-03-29_at_12.53.18](/uploads/426e603675171f0dc4e0af83c7762eba/Screen_Shot_2016-03-29_at_12.53.18.png)

![Screen_Shot_2016-03-29_at_12.53.13](/uploads/645ad7955acfb9f7693245fcc048ee49/Screen_Shot_2016-03-29_at_12.53.13.png)

See merge request !3228

This makes it easier to query, simplifies the code, and makes it
possible to figure out what transaction the data belongs to (simply
because it's now stored _in_ the transaction).

This new setup keeps track of both the real/wall time _and_ CPU time
spent in a block, both measured using milliseconds (to keep all units
the same).

Closes #15128

Remove `random_markdown_tip` helper

Only usage got removed in !3442

See merge request !3637

Correct documentation on enabling artifacts.

The docs say to enable artifacts that settings should be set to "false".  This updates the documents to change the setting to "true".

See merge request !3630

Removed important from css