Changed the response for canUse to return an error code because the
error could be different depending on the reason. For tabComplete no
error is shown, but for commands, the error can be shown.
Implemented the invite and uninvite commands and filled in the team
command.
* Added more database functions.
Added ability to check if a uniqueId exists without creating it - used
to check if a player is known or not.
Added join/quit listener.
* Hooked in grid database to track where islands are.
Added Nether events and portal function.
Added default /island command operation.
* Added protection for islands.
* Updated license to BSD license.
* Removed unused imports.
Added configs.
* Added more protection listeners.
Flying mobs, visitor protection
