Spectating

Add more functionalities to the spectate command to let servers create a real audience for tournament battles.

Ex: add target selectors and a "range" argument to the /spectate command, to let server admins force all people in an area to spectate the same battle.
Allow people to spectate a battle by clicking Y while looking at another spectator, so if new players join the audience they don't have to go down to the arena to become spectators.

It would also be nice to have a cheering system or a betting system in the UI, but I'm not sure how beneficial they would be.