Add group membership api

Change-Id: I5b174bba02856ede788dcb51ec9b0d598ea7d0df
Fixes for @randx

Change-Id: I3b15ae34c0957a0f4026e1886c92a9770e9d170e
Merge pull request #4990 from karlhungus/feature_group_membership_api

Add group membership api
Fixed description.
Fixed Import Bare Repositories instructions to match rake task.
Forgot to fix the comment instructions.
Merge pull request #5013 from clayzermk1/master

Import Bare Repositories instructions/description are incorrect
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.
Merge pull request #5014 from bladealslayer/feature/big-commit-improvements

Improved large commit handling.
Drop support of root namespace in routing