Implement new GMCP fields that MUME supports

[Kaspar-Metsa]

• News 2703

GMCP Core.Vitals now also contains the name of your opponent (in the opponent field) and the one they are fighting (in the buffer field).
GMCP Room.Chars character fields now have an "opponent" flag on your current fight opponent.

• The "Room Panel" and "Group Panel" should show new column "Opponent" that contains the name of the opponent if there is one.

• News 2701

New fields were added to the GMCP Char.Vitals messages: mount-moves, opponent-hits, buffer-hits, and position.

• The "Room Panel" and "Group Panel" should show new column "Opponent hits" that contains the HP of the opponent if there is one.