- Fixed Event work incorrectly from non-static HandlerList

Minor Patch
- Added isOffHanded to PlayerRightClickEvent to check offhand event

New Features
- Added Player/Entity/block operator get/set/minusAssign to set metadata easily
- Added Event#callEvent (Self-returning)
- Added Listener#register
- Added isBlockInteraction variable to PlayerLeftClickEvent/PlayerRightClickEvent

Bug Fix
- Fixed PlayerLeftClickEvent is calling instead of PlayerRightClickEvent

- Added Metadata utility method to Entity, Block
- Added cancellable scheduler utility

- Fixed AIR interaction failed on event triggered