Improve performance of user profiles, finding groups, and finding projects
This MR improves the following:
* Rendering of profile pages and Atom feeds
* Finding groups (using GroupsFinder & friends)
* Finding projects (using ProjectsFinder & friends)
Initially this MR was intended to only improve rendering of Atom feeds, but over time other fixes were introduced as well as the same code was the cause of all these problems.
See merge request !1790
Improve performance of user profiles, finding groups, and finding projects
This MR improves the following:
* Rendering of profile pages and Atom feeds
* Finding groups (using GroupsFinder & friends)
* Finding projects (using ProjectsFinder & friends)
Initially this MR was intended to only improve rendering of Atom feeds, but over time other fixes were introduced as well as the same code was the cause of all these problems.
See merge request !1790
Add option to mirror an upstream repository.
Closes internal https://dev.gitlab.org/gitlab/gitlab-ee/issues/279
Depends on gitlab-org/gitlab-shell!29
To do:
- [x] Decide on what user should be the author of the activity feed events. The initial project creator perhaps? That makes sense for personal projects, but less so for group projects, where it's even possible that the creator has since left the team.
- [x] Write specs!
- [x] Write documentation
- [x] Port back relevant commits to CE: gitlab-org/gitlab-ce!1822
----
## Mirror status on project homepage

## Settings navigation item

## Mirroring settings

## Activity feed with new "pushes" (mirror updates)

I have yet to decide on what user should be the author of these events. The initial project creator perhaps? That makes sense for personal projects, but less so for group projects, where it's even possible that the creator has since left the team.
## Warning that branch has diverged from upstream

## Commits heading after failed update

Link send user to the mirroring settings if they are a project admin.
## Mirroring settings after failed update

## New project page

## Import form after failed import
(Screenshot outdated)

Shown when the initial import of a project fails, not when an update of an existing project fails.
cc @dzaporozhets @sytses @JobV
See merge request !51
This class can be used to join multiple AcitveRecord::Relation objects
together using a SQL UNION statement. ActiveRecord < 5.0 sadly doesn't
support UNION and existing Gems out there don't handle prepared
statements (e.g. they never incremented the variable bindings).
Refactor complex methods
Make flog part of CI check which is not allowed to fail. I used high score (70) and refactored most complex method. In future releases we should lower acceptable score to something like 40..50
Part of #3444
See merge request !1794