In the event that the branches list has a 'HEAD' ref and the user is
an admin, allow them to change the revision.
- If a user is not an admin, they will not see any buttons
- If a user is an admin, they will see an 'edit' button, when clicked
an input displays with the current revision value. They can save or
cancel.
- If they save and the input is invalid, an error toast appears
(from the error manager) and the input remains open.
- If save succeeds, the value is updated, and the input/save/cancel
buttons disappear, in favor of the original text and edit button.
Change-Id: I923e106d6b4eb47ec8cd251955d2f5ece180cce4
8990a7df97