EE Port: Honor the "Remember me" parameter for OAuth-based login

See merge request !2175

Check license for milestones on issue boards

Closes #2568

See merge request !2315

Introduce namespace license checks for Push Rules (EES)

Closes #2573

See merge request !2335

Clarify when Code Quality shows in MR widget

Closes #2782

See merge request !2298

Namespace license checks Issue & MR template

Closes #2580

See merge request !2321

And separate EE/CE for board.rb

Introduce namespace license checks for merge request approvers (EES)

Closes #2566

See merge request !2324

# Conflicts:
#   app/models/license.rb

Hide Focus mode button if feature not available in license

Closes #2569

See merge request !2303

Namespace license checks for Contribution Analytics (EES)

Closes #2579

See merge request !2302

Fix EE conflicts for "Allow unauthenticated access to the `/api/v4/users` API"

See merge request !2247

When the Issuable Default Template feature is not available, do not
show the input form to configure the Issue & MR templates on the
Settings page.

Only when the Issuable Default Templates feature is available, fill in
the description from settings when building a new MR.

Only when the license allows Issuable Default Templates, set the issue
description when building an Issue.

Do this by splitting out EE-specific features into
EE::Issues::BuildService. And also split up spec files.

- Don't use `request.env['omniauth.params']` if it isn't present.

- Remove the `saml` section from the `gitlab.yml` test section. Some tests
  depend on this section not being initially present, so it can be overridden
  in the test. This MR doesn't add any tests for SAML, so we didn't really need
  this in the first place anyway.

- Clean up the test -> omniauth section of `gitlab.yml`

- Disable an ESLint check rather than work around it (by
  converting `OAuthRememberMe` from a regular class to a
  static class.

- Scope `$` calls inside `OAuthRememberMe`

- Change double quotes to single quotes.
- Why is `OmniAuth.config.full_host` being reassigned in the integration test?
- Use `map` over `map!` to avoid `dup` in the `gitlab:info` rake task
- Other minor changes

- The test for `rake gitlab:env:info` executed the rake task, which mutated the
  list of omniauth providers, breaking subsequent tests relying on this list.

- I've changed the rake task to duplicate the providers list before modifying it.

- I tried to get this to work by stubbing out portions of the config within the
  test. This didn't work as expected because Devise/Omniauth loaded before the
  stub could run, and the stubbed config was ignored.

- I attempted to fix this by reloading Devise/Omniauth after stubbing the
  config. This successfully got Devise to load the stubbed providers, but failed
  while trying to access a route such as `user_gitlab_omniauth_authorize_path`.

- I spent a while trying to figure this out (even trying
  `Rails.application.reload_routes!`), but nothing seemed to work.

- I settled for adding this config directly to `gitlab.yml` rather than go down
  this path any further.

- Added saml, authentiq, cas3, and auth0
- Crowd seems to be a special case that will be handled separately.

- There was previously a test for `saml` login in `login_spec`, but this didn't
  seem to be passing. A lot of things didn't seem right here, and I suspect that
  this test hasn't been running. I'll investigate this further.

- It took almost a whole working day to figure out this line:

    OmniAuth.config.full_host = ->(request) { request['REQUEST_URI'].sub(request['REQUEST_PATH'], '') }

  As always, it's obvious in retrospect, but it took some digging to figure out
  tests were failing and returning 404s during the callback phase.

- Test all OAuth providers - github, twitter, bitbucket, gitlab, google, and facebook