Hierarchical tag: done

Hi,

As discussed before the 2.1 feature freeze and thanks to the addition of the parent_id tag, I've been able to handle "main" and "second level" of tags (tree with two levels so far).
http://forum.civicrm.org/index.php?topic=3899.0

To make it sexier, I've added an ajax interface on the tag tab in the contact, where you can directly add or remove a tag. I've done it using the rest interface.
http://forum.civicrm.org/index.php/topic,5585.0.html

As said, I've had to add various things here and there, and that's very much work in progress, but i'm happy to svn share if you give me access.

X+