And create new Project#requesters, Group#requesters scopes.

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

Add Todos API

* Closes #14068
* Closes #14675 

- [x] Implementation
- [x]  Tests
- [x] Documentation
- [x] Changelog

See merge request !3188

Fixing problems with events for import/export

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/19202

A couple of issues related to target being missing in exported `Events` (as being polymorphic and not have `ActiveRecord` relationships is a bit more tricky than normal models) plus as the export was in JSON, the import retrieves hashed fields as stringified hashes and not symbolized - so fixed that as well, which was the cause of https://gitlab.com/gitlab-org/gitlab-ce/issues/19202

Also fixed / refactored tests
:simpl
Import/Export Version has been bumped to 0.1.1 as theses changes to events won't work very well with old exports - forcing users to generate a new export in the new version.

See merge request !4987

Upgrade sprockets and sprockets rails, remove quiet_assets

## What does this MR do?

Upgrade Sprockets from 3.6.0 to 3.6.2.

Changelog: https://github.com/rails/sprockets/blob/3.x/CHANGELOG.md

Upgrade Sprockets Rails from 3.0.4 to 3.1.1.

Changelog: https://github.com/rails/sprockets-rails/compare/v3.0.4...v3.1.1

quiet_assets has been seemingly abandoned, and now sprockets-rails has the feature built-in!

The config was added in this PR: https://github.com/rails/sprockets-rails/pull/355

Working towards #14286.

See merge request !5029

Ensure that branch and tag names are given in API

## What does this MR do?

It ensures that the tag or branch name is given. @rymai We talked in an earlier MR about this.

See merge request !5012

Cache autocomplete results

## What does this MR do?

Caches the results of the autocomplete AJAX call to stop new GFM inputs on the page from requesting new data. The cache is then cleared on each new page so that it doesn't stay around per project.

See merge request !5043