[WIP] Create merge request when editing on web UI.
Created by: cirosantilli
Fixes ACCEPTING MR at: http://feedback.gitlab.com/forums/176466-general/suggestions/5350102-option-to-make-a-merge-request-when-editing-via-we
If user has push permission:
After clicking the fork checkbox the branch name input appears. It will be prefilled with a branch name of form patch-N which hasn't been used yet.
If the user does not have push permission, the checkbox is checked and disabled: he must fork.
If this is OK so far I'll continue.