[Village] Add townCenter property.
[Village Manager] Add 'getTownCenter()'.
[Entity] Reorder properties. Add cheap type comparison.
[Entity Manager] Utilize villageManager.getTownCenter()
(++ NEW FILE ++) Created 'ObstructionMap' class.

This class just stores whether there's an obstruction on a tile.
This class implements the all-important 'findOpenPosition' method.
[SDL Widget Container] Remove unneeded output.
[Entity] Re-order the entity types and add some flag enums.
[Entity] Add EntityGroup calculation based on EntityType.
[Main] Actually seed the RNG instead of always passing '0'.
[Position] Add D_NORTH, D_SOUTH, D_EAST, D_WEST.

These are compatible with existing directions; either terminology can be used.
(+++) [Entity Manager] Utilize obstruction map. We can make buildings now!

TODO: Resource availability.
TODO: Job creation.