Add Minecart

Added interface for Vehicle and minecart.
Vehicle can be used for boats as well, it allows you to apply a velocity to the entity, which is what vehicles use to move, unlike regular entities.
@kenzierocks the blick is in the meta data of the entity.
It is not actualy an entity, see http://dev.bukkit.org/media/images/60/870/hangraillogo.png
It is a cart, with a creeper in it and stone wall as block set in the meta data.

I did indeed forget offset