Add Entity

Added entity class with most field getters and setters.
Will support mods as long as the entity type can be modified by the server at any time.
@amaranth People what have databses that store entity id's probably would like to see it.
Recoding your plugin is one thing, rebuilding the databse is another.
Sure i can make it getID if thats prefered, and i wouldn't know what to put for javadocs instead.