Add a dropdown to filter and sort projects in the dashboard projects & group pages (!2568) · Merge requests · GitLab.org / GitLab FOSS

Addresses #3968 (closed), #3245 (closed), #3799 (closed). This MR is bigger than I expected but I don't think this could be split into smaller MRs.

Notes:

I replaced "Last updated" by "Recently active" since the underlying field used with this sorting method is last_activity_at which is the time of the most recent project's event. I thought it was not very useful to sort by updated_at (which is updated when the project settings itself is updated) because from a user perspective the goal is to see the most recently active projects, not the most recently updated.
I used the Project's personal scope for the "Owned by me" filter.
I did not show the "Owned by" filters in the group page since it doesn't make sense: group's projects are owned by the group.
The group page has been split in two real pages (instead of loading the activity feed and the project lists on one page) since sorting reloads the page, it was cleaner to do it like that. The two pages are /groups/:group -> group's activity (same as before) and /groups/:group/projects -> group's projects. The former /groups/:group/projects route has been changed to /groups/:group/projects/edit which is more appropriate IMO.