Advanced cache

Fixes #1993

* Build missing cache values in background job after each push
* Store commit_count in project table. Refresh in background job
* moved repository size calculation in background job


## Advantages

Every time push is triggered - we build cache for project even without user visiting project page. 
That means first visit is as fast as others now. This is especially good for active projects where people have some requests fast because of cache and some slow - because cache was build in their request. 

Between cache expired and cache built we we had gap when Linux repo can give 502 error because calculation commits count takes 30 seconds or even more. 
Using value from database fix this problem. Before cache is updated you see old value from database. After - you see new one. 

Basically this merge request is super win to GitLab. We don't do some heavy operations in user request but instead in background job. 

## Temporary problem

After this migration all projects will have `0` commits in database. It fill be replaced with real value on next push. I did not add recalculation to migration because it will last forever on big instances.  Can be fixed by adding rake task which will go in background on live instance without downtime

See merge request !986

The release manager owns the stable branches

I think this helps the release manager because it means they don't
have to worry about others pushing commits at the last minute.

See merge request !1907

Expire Rails cache entries after two weeks

This should help prevent endless Redis growth.

See merge request !1903

I think this helps the release manager because it means they don't
have to worry about others pushing commits at the last minute.

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

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

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

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

Added note about chef

Added note about chef being required to generate GitLab config. because of tweet https://twitter.com/grahamgilbert/status/621015318442459136

See merge request !982

Added new doc about creating a new branch

Added new document about creating a branch and fixed bullets in all the other documents. Also fixed "git push REMOTE BRANCH".

See merge request !1894

Document should start from h1 title. Also put badges on top for easier tracking

Looks much better with new project page design. 

See merge request !983

Time ago fix for branch compare page

https://dev.gitlab.org/gitlab/gitlabhq/issues/2508

See merge request !1904

This should help prevent endless Redis growth.

Remove author information from "post" in merge_requests API.

api: expose work_in_progress flag

See merge request !948

Fix docker image

See merge request !979

This reverts commit 8a01a122.

fixed notifications title

I fixed the title and link to this document because I believe that it's more clear and easier to find if it has "emails" in the name.


See merge request !1897

Fix path to move_drop_indexes.ed

Small documentation fix.

See merge request !1900

Add nice scroll for sidebar
Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

See merge request !978

Hide scrollbar from sidebar when external mouse is connected to OSX

See merge request !977

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

create update guides for 7.13



See merge request !1899