- First batch of profile module improvements:

   + Tidied up the profile configuration page: grouped form elements.

   + Tidied up the block configuration settings: removed hard-coded
     table.

   + Changed the profile API to return the preferred group name, and
     changed the user module to group settings.  Modules implementing
     the _user hook will need to be udpated.

   + Removed register_form and register_validate for now.