Adds basic "collision" detection, sprite sheets

Implements a system to check to see if a part of the map is currently
occupied by a building. Also adds a specialized cursor, various sprite
sheets, and some animation update logic.
Building Placement Logic + Grid

Building placement is fixed to solve the problem of overlapping
buildings. Additionally, the mouse now operates in grid units of 10, for
ease of placement when one is attempting to place buildings adjacent to
one another.