This MR adds a string (thus max 255 chars) field to the enviroments
table to expose it later in other features.

Submit new issues created via the WebUI or API to Akismet for spam check on public projects.

## What does this MR do?

Submit new issues created via the WebUI by non project members to Akismet for spam check.

## Why was this MR needed?

Support for Akismet was added only to the API with !2266. This MR builds on that functionality to also check issues submitted via the WebUI for spam.

## What are the relevant issue numbers?

Related to:

- #5573 
- #5932 
- gitlab-com/infrastructure#14
- gitlab-com/support#61
- !2266

cc @stanhu @MrChrisW 

See merge request !5333

Pass an array of user IDs in the `skip_users` param to have them
excluded from the results (unless they are explicitly included through
the `current_user` or `author_id` params).

A release's tag reference is just the name of the tag, not the entire
tag object.

This also fixes the tags index if a tag's message contains non-UTF8 byte
sequences.

Add support for inline videos in issue, MR and notes (on issue, commit, MR, and MR diff)

## What does this MR do?

It adds support for inline videos in issue, MR and notes (on issue, commit, MR, and MR diff). Most of the work was done by @hayesr in !3508 but a few improvements were still missing.

## Why was this MR needed?

To be able to play uploaded videos in GitLab!

## What are the relevant issue numbers?

Closes #4142.

## Screenshots

### Video players

![Screen_Shot_2016-07-19_at_18.44.09](/uploads/e85e531b455a41c3e66b26b356abaafd/Screen_Shot_2016-07-19_at_18.44.09.png)

-----

![Screen_Shot_2016-07-19_at_18.44.29](/uploads/05f52a812760210d1eae86a7f8fc48bc/Screen_Shot_2016-07-19_at_18.44.29.png)

-----

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [x] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- Tests
  - [x] Test `VideoLinkFilter`
  - [x] Test in `spec/features/markdown_spec.rb`
  - [x] Improve `spec/uploaders/file_uploader_spec.rb`
  - [x] 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 !5215

Add a test to make sure the help page UI path doesn't break in the future.

Fix #19972 and #19889.