Item12907: hide category factory when there are no categories

also:
- fixed freshly created categories can't be reparented
- added $count to %HIERARCHY to count number of categories
- fixed depth param to %HIERARCHY not to decend on a zero depth




git-svn-id: http://svn.foswiki.org/trunk/ClassificationPlugin@17682 0b4bb1d4-4e5a-0410-9cc4-b2b747904278