Fixed conflicts with other plugins with a restricted chat.
Fixed Javadoc (in SpectateApi.setArenaForPlayer()).
Moved the registration of the Arena class as a serializable one in the onLoad method of the main class.

Because in some rare cases, registering this in the onEnable method can cause problems. With this we're safe.
The spectators can see read-only GUIs for the chests, etc.

Without chest opening animation.
Merge pull request #13 from AmauryCarrade/misc

Bug-fixes & Chest viewing for specs