Revision single and diff view

Needs a little bit more testing and clean up.  Single view now only
renders the content of a single revision.  Interactions like edit,
moderation has been removed, users are not supposed to perform these
actions in here.  Replies to post have also been removed.  This is
history revision view while the replies are always the latest revisions.

Change-Id: I533da49a42d186c1958bab0b26147f8522ba30ed
Merge "Revision single and diff view" into frontend-rewrite