Add labels api authorization. Update permission doc

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>
Use new git max_size in the settings initializer
Merge branch 'git_max_size' into 'master'

Use new git max_size in the settings initializer

This allows us to avoid repeating default max_size setting in the omnibus-gitlab repository.

See merge request !1021
Merge branch 'label-permissions' into 'master'

Label permissions

* Update label permission docs
* Add authorisation to labels via API

See merge request !1020