More coloring modes

[mjrlowe]

Currently we have two coloring modes: "normal", which is just one color, and "distance", which colors the cells according to the distance from a certain point.

Here are a few ideas for some other coloring modes that might work well:

• Number of neighbors
• Number of times visited
• Direction (or direction bias if that ever gets added)
• Set (particularly for Kruskal's but could work for other algorithms like Eller's)
• Order added/connected
• Order you would pass them if you went from the start using the left/right wall following method.