Implement different Markdown rendering pipelines and cache Markdown

Builds on !1090. 

Related to !1014.

Fixes #2054.

See merge request !1602

Block LDAP user when they are no longer found in the LDAP server

Currently, if a user is deleted from LDAP the `Gitlab::Ldap::Access.allowed?` method will return `false`, but the user will not be blocked. This means that the user would be able to continue using GitLab if they are already logged in, or when performing Git over SSH operations.

After this change, users will be blocked when they no longer exist in LDAP. There is still a one hour LDAP check cache time in effect, so the change is not immediate. This is noted in the documentation.

cc/ @DouweM @dzaporozhets 

See merge request !2022

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

Update project repository size and commit count during import:repos task

Closes #3848

See merge request !2011

Closes #3848

Build related UI fixes

## Before

![Screen_Shot_2015-12-08_at_13.15.21](/uploads/b72ed55da1f0ec953d2eb077fa4fbb18/Screen_Shot_2015-12-08_at_13.15.21.png)

## After

![Screen_Shot_2015-12-08_at_13.15.01](/uploads/144d8099e2724a51125e392dcbd43ed4/Screen_Shot_2015-12-08_at_13.15.01.png)


See merge request !2015

Fix broken group avatar upload

Closes #3918

See merge request !2018

Languages graph

See merge request !2009

UI: Add "New X" buttons to dashboard and group issue, MR and milestone indexes

# To do

- [x] Use searchable dropdown since dashboard/group can have a lot of projects. Use select2?

## Before

![Screen_Shot_2015-12-07_at_17.26.52](/uploads/22c6d6df10414f9e3e35d6cea3870486/Screen_Shot_2015-12-07_at_17.26.52.png)

## After

![Screen_Shot_2015-12-07_at_17.26.33](/uploads/02d082490ed6c83c66f052a5b601b5be/Screen_Shot_2015-12-07_at_17.26.33.png)

As you can see, for milestones, groups are listed as well as we can now easily create group milestones.

Fixes #3544 and https://dev.gitlab.org/gitlab/gitlabhq/issues/2581

See merge request !1968

Sync all repos

Scripts and documentation for moving repos, used on gitlab.com.

See merge request !1439

Added 3  rake tasks for repository maintainance

## What does this MR do?
This MR adds 3 rake tasks

- gitlab:git:repack
  - `-a`
  - `--quiet`
- gitlab:git:gc
  - `--auto`
  - `--quiet`
- gitlab:git:prune
  - Needs git version > 1.8.4.1, Ubuntu repos @ 1.9.x

## Are there points in the code the reviewer needs to double check?
AFAIK this MR abides by the Guidelines for shell commands. Also, the output given is not the diskspace saved etc, just if the commands were succesfull. (Parsing output etc did not seem like the way to go)

Output might be verbose when a lot of repo's are in the system?

## Why was this MR needed?
`git gc` and `git prune` can reduce storage space used.

## What are the relevant issue numbers / Feature requests?
Closes #1529

## Screenshots (if relevant)
`rake -T`
![Screenshot_from_2015-09-22_14-57-59](https://gitlab.com/zj/gitlab-ce/uploads/4abfa00ce7afcc73f553d92581246731/Screenshot_from_2015-09-22_14-57-59.png)
(git fsck now removed as IMHO it doesn't add any value.)

See merge request !1388

Closes #3918

Fix signin with OmniAuth providers

OmniAuth CSRF protection was broken with the move to Rails 4.2 since
the CSRF logic in Rails changed. 

This new implementation calls out to Rails instead of copying its code,
which is far easier to maintain.

See merge request !2019

Bump gollum-lib to 4.1.0 and fix dependency mismatch with rouge

Closes #3767

See merge request !2017

Serve LFS object

Depends on gitlab-org/gitlab_git!57

See merge request !1976

Closes #3767