Implemented a system to load tilemap files

- The Textures class has also been renamed to Resources as it now houses
loaded maps.
- There are three new projects in the solution now:
- TilemapLib: Content pipeline extension library that allows for a
custom importer for tilemaps
- BlankMapGenerator: A basic console based application that makes
tilemaps. This is a temporary solution, eventually the maps will be made
from within the game.
- TilemapImportDebug: A project that was used during the testing of the
map format. It is redundant but I have kept it because some of its
functionality might be reusable later on.

-NOTE: as of this commit, the tilemaps that have been loaded have not
been tested, so there is a chance that most of what has been done this
commit could be re-done.