Create a dedicated revert permission to only allow specific groups to
revert changes. Groups that don't have the "Revert" permission will not
see the Revert button and will not be allowed to revert changes from
the GUI.
This change is created due to spammers that easily use the "Revert
Submission" button to create many changes quickly.
Change-Id: If5180bc982659ab5c9ddaa096ac455823484c50c