Splitted up the taxonomy_delegate_mycategories function and added a theme function

The entire category modification system for the delegated admin was made in one function. I've splitted the function (and the menu entry) in several menu entries. By this the menu system will create the correct breadcrumb and menu trails.

I've also added a theme function for one of the pages, probably all pages should have theme functions but at the moment i've only created the one that i needed.

Don't know if these changes are useful, but i created a patch from the last dev version.