[dev] Group class and Datatree

[Edward Rudd]

Why exactly is the Horde_Group class tied so closely to the DataTree class?
Wouldn't it be better to move the public Datatree_Group functions to the
Horde_Group interface?  

example: in horde/admin/group.php the
$groups->_datatree->get(DATATREE_FORMAT_FLAT, -1, true) is called instead
of a more generalized $groups->listGroups();  and later
$groups->_datatree->getParent($groupname) is called instead of calling a
$groups->getParent($groupname);  

It would seem a better design to have the Group interface be less tied to
the Datatree so that full replacement backends can be written easily (in
my case an LDAP backend for managing groups).