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 It is a class per minecarft function.
the command block has its own special logic attached to it, like executing commands and allowing to open command block gui on right click.
Allthough you can spawn a command block minecart with an air block inside of it (you wont see the command block) without attaching another entity to it