Add a tags page to the revision view

[Daniel Schierbeck]

The revision view should have a tags page, allowing the user to view the current set of tags associated with the revision, and adding, deleting and renaming tags.

The UI could be something like this:

  ## *Tags*
  ## There are 2 tags on this revision
      .------------------------------.
      | @ release-1.0.2 | [ Add Tag ]
      | @ foobar | [ Edit Tag ]
      | | [ Remove Tag ]
      '------------------------------'

[Daniel Schierbeck (dasch)]

Hmm, no luck with the formatting, but you get the idea.