Add map tiles

[Anonymous4045]

We need to add in the base sprites that the levels are made from. These must be png images that are 32x32 pixels (or smaller).

These should include the grass blocks (or other background blocks) and path blocks that the enemy cats will follow.

These images can then be used in the Tiled map creator to construct various levels. All of the towers the user builds and the enemies that spawn cannot be placed in the editor, so those shouldn't be included here.