Refactor: using an enum to store the current SpectatorPlus' mode (any/arena).
Fixed potential NPE in SpectateAPI.isSpectating().

If this method is called in a join event, before the one of SpectatorPlus.
Changed the riority of the join event.

To handle better plugins using the API in join events.
Added a WORLD SpectatorPlus' mode.

With this mode, the spectators will be able to teleport themselves to all players in the same world.
Useful for minigames servers.
Hidden spectators are displayed for admins in arena mode.
Merge remote-tracking branch 'origin/master'

Conflicts (fixed):
	SpectatorPlus/src/com/pgcraft/spectatorplus/SpectateCommand.java
Add an actual teleport back into the arena's boundary (Message is
printed to console when teleported still for debugging purposes).
Merge remote-tracking branch 'origin/arenaLimit' into arenaLimit