We should add a Tile layer so that we can more easily change the configuration of a room, and eventually design room-building tools and whatnot.

Tiles should have:

• A background image (irr::video::ITexture*)
• A pointer to the active sprite (or NULL if there is no sprite on this square)
• a function that returns a boolean representing the observational state
• a function that increments an internal value that represents the observational state - to be used when an observational 'ray' intersects the tile
• a function to render the whole tile at once

TileLayer should have:

• A 2D collection (std::vector, maybe? I need to look up the appropriate way to achieve this) of Tile pointers - NULL
• a function to render the whole layer at once