Comment 2 for bug 161982

The attached patch provides a fix for this. I tried to respect the prevalent coding styles as good as possible.

Roughly the patch does the following:
  * Make all tags the same size
  * Tags that have no documents are grayed out
     * All other tags are displayed in the format "tagname (tagusecount)"
  * Add a separator that divides 'All' and 'Untagged' from the rest of the tags

The patch also fixes several minor issues:
  * After renaming, tags are only marked as dirty if oldname != newname
  * Make the 'All' and 'Untagged' tags immutable