Collision systems

[chrislloyd]

Basically add width and height properties to the position components. For 99% of entities they'll be 1x1, but it could allow for larger entities. This data can be used for collisions.

The next thing is figuring out how to potentially block moves. A few ideas:

1. Have movement in a "potential move" move component, and have the collisions system actually apply and resolve those moves.
   2.Hurt all living entities that collide with other entities.

The hurting way is simple, but mightn't be expected (and might lead to weird gameplay).