Better tag overview on the new/edit contact page

I think the tag overview of the page for the existing contact (jstree) looks way better than the boring list on the 'new Contact' page... So I ported it. :)

I also implemented the existing option to disable checkboxes for tags with 'is_selectable'=0.
(works best with #4194)

Forum topic:
http://forum.civicrm.org/index.php/topic,33934.0.html