Update User api to respect default settings

Change-Id: Ia723321a5cb05deb626d34c7d8d78194e049b1f0

Change-Id: Ib4eb533dff5c722fe559330e4aa71b5d5baf6fb8

-calling build_user will now apply defaults and only override them if as: :admin is set

Change-Id: Id1d938c0967752ecc14370af54f2d88128d18c44

-API now respects default_projects_limit, default_can_create_group, and default_can_create_team

Change-Id: I059d060d576df1050e5371e707381c5e8c608a7a

Fix user.several_namespaces? to work with multiple ownership of groups

Add link to project page from admin view

-i flag allows sudo to work for git users using rvm that is not being us...

make public/private setting for project creation configurable

API: admin users can sudo commands as other users

Change-Id: I966bfd0ccc4b05925384ecab8c6cbe3c6ba3b667

Change-Id: I305266fe9acbbb5136adeeb52e7e4e1d6629a30a

-Specifying a header of SUDO or adding a :sudo with either user id, or username of the user will set the current_user to be that user if your identifying private_token/PRIVATE_TOKEN is an administrator token

* added description
* simplified form
* enabled gfm autocomplete

Improved large commit handling.

Previously, only number of changed files mattered. Now, number of lines to render in the diff are also taken into account.

A hard limit is set, above which diffs are not rendered and users are not allowed to override that. This prevents high server
resource usage with huge commits.

Related to #1745, #2259

In addition, handle large commits for MergeRequests and Compare controllers.

Also fixes a bug where diffs are loaded twice, if user goes directly to merge_requests/:id/diffs URL.

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