Implement Order-Robot matching

[galacticglum]

Every time step, the warehouse should try to match available Robots to orders that need to be fulfilled. This can be done through a variety of metrics: take the closest robot, take the first robot, etc...

When a Robot is matched, it can compute a route to the destination using a routefinder algorithm. Then, the route can be visualized.

[galacticglum]

This will need to be integrated with the order handling system (see #43). One key question to consider is whether all orders have to be assigned to a Robot (e.g. should some orders not be handled by robots?)