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.
There's also an inherit flaw here: Normally, to set any block, you have a `FallingBlock` entity ride the `Minecart`, but for the functional ones it's actually a different entity. This probably works fine as this implementation side, but it might be worth noting.