Remove metasets, overlays for gnome2.  Renamed Gnome3 metaset and ports-...

...overlay to Gnome.  Moved xession for mate to 02Mate to replace Gnome.  Moved Gnome3 to 31 to replace where Mate was in the order.  Changed pkg-parents for Gnome & Cinnamon to Unsupported Desktops.  While technically these are both XDG complaiant Cinnamon does not work without 3D.  Gnome 3 also has many broken programs.