* upstream/master: (117 commits)
  spec and fix for sanitize method
  remove fix validatable import url migration
  Fix typo in spec
  Update Gemfile.lock after versions were added in !5078
  Add more comments to regex
  Add changelog item
  Add blockquote fence syntax to Markdown
  Fix typo and explain the precedence of STDERR and STDOUT
  Add changelog entry for !4399
  Add reminder to not paste private SSH keys
  Make subnavigation a bit darker color
  Update ui_guide.md with button capitalize rule
  Re-use queries in reference parsers
  Use btn-danger for delete button.
  Update New Snippet buttons.
  Run bundle install.
  Add min attribute to project_limit field on user's form
  Wrong gitlab-shell version
  API: Expose shared projects in a group
  Memoize MR merged/closed events retrieval
  ...

So we redirect from ref and build_name to the particular build, namely:

* /u/r/artifacts/ref/build_name/* -> /u/r/builds/:build_id/artifacts/*

For:

* download
* browse
* file

Fix typo in factory for projects.rb

## What does this MR do?

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

## Why was this MR needed?

## What are the relevant issue numbers?

## Screenshots (if relevant)

## Does this MR meet the acceptance criteria?

- [ ] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [ ] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- [ ] API support added
- Tests
  - [ ] Added for this feature/bug
  - [ ] All builds are passing
- [ ] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [ ] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [ ] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !5100

Add reminder to not paste private SSH keys

## What does this MR do?

Just got the "How would you make GitLab better?" mail and thought that I could follow it.

This commit adds a short reminder to not paste the private part of an SSH key to the form where one can add SSH keys to one's account. I think that's an useful message, both for people who aren't that experienced yet and for people who are sleep-deprived. :-)

I decided to just list the most common key type, `ssh-rsa`. The full list of key types in the [CVS repository of OpenSSH](http://cvsweb.openbsd.org/cgi-bin/cvsweb/~checkout~/src/usr.bin/ssh/sshkey.c?rev=HEAD&content-type=text/plain) contains some types which I'd regard as a bit obscure. Mentioning all of those types would probably clutter the form too much. We could think about whether to list what is probably the second most common key type, namely `ssh-dss`. But note that this key type [seems to be deprecated](https://security.stackexchange.com/questions/5096/rsa-vs-dsa-for-ssh-authentication-keys).

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

I didn't actually test this one-line change.

## Why was this MR needed?

It's not, strictly speaking, needed, but could be considered a nice addition.

See merge request !4399

Remove slow migration and add fix to sanitize errors

Getting rid of the slow migration and preventing the Error to occur

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/19608

See merge request !5176

Run bundle install and update Gemfile.lock

!5078 didn't update the `Gemfile.lock` even though it added some restrictions on gem versions, this fixes that.

cc: @rymai 

See merge request !5159

Fix commit avatar alignment in compare view

Closes #19567 

See merge request !5128

Add blockquote fence syntax to Markdown

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/16564

Before Markdown rendering happens, this will transform this:

```
Let me quote this here email:

>>>
Dear friend,

How are you?

Greetings,

Me
>>>
```

Into this, saving me from having to prefix all of those lines with `>` manually when I copy some multiline text from another medium:

```
Let me quote this here email:

> Dear friend,
> 
> How are you?
> 
> Greetings,
> 
> Me
```

See merge request !3954

Update Gemfile.lock after versions were added in !5078

See merge request !5171

Bump google-omniauth-oauth2 to 0.4.1

Closes #19064

See merge request !4882

Re-use queries in reference parsers

This MR changes the reference parsing pipeline to cache queried objects and re-use them on subsequent runs. Data is cached in the `RequestStore` module so it's automatically flushed after a request.

Certain references are processed multiple times. For example, for every system note we check if it's a cross reference by getting the issues, MRs and commits it references. When redacting data we may end up querying these very same objects. By caching this we can quite drastically reduce timings and SQL query counts.

#15607

See merge request !5020

Fix typos in API documentation

See merge request !4949

Fix phpunit command in the docker example.

Closes https://gitlab.com/gitlab-org/gitlab-ci-multi-runner/issues/1478

See merge request !5147

Fix wrong gitlab-shell version in 8.9-8.10 update guide

See merge request !5153

Fix typo and explain the precedence of STDERR and STDOUT

## What does this MR do?

Addresses comments https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/5088#note_12884564

See merge request !5169

Make subnavigation a bit darker color



See merge request !5166

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Update ui_guide.md with button capitalize rule

cc @jschatz1 @hazelyang @skyruler 

See merge request !5161

This caches various queries to ensure that multiple reference extraction
runs re-use any objects queried in previous runs.