[WIP] I parameterized all the Entity abstract subclasses.

Entity and its other abstract subclasses (LivingEntity, NonLivingEntity,
etc.) have now been parameterized to allow the protected method
`getEntityMC()` to return the Minecraft Entity object casted to the
appropriate form for easy use in utility methods.

Signed-off-by: REALDrummer <conman.davey@gmail.com>