Better tag overview

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.

This is the third try.
Hope this one stays clean :)

Forum topic:
http://forum.civicrm.org/index.php/topic,33934.0.html
Issue:
https://issues.civicrm.org/jira/browse/CRM-15180