Easier Footprints.

* Add FootprintType enum
* Add <char, FootprintType> dictionary
* Add TilesOfType method to FootprintUtils
* Remove (now obsolete) UnpathableTiles

This was meant to be groundwork for another feature I'm working on but it is late and I cannot remember the ultimate goal ATM, so I am proposing this which allows creating and querying footprint types in an easier manner.