! WIP: Preparing to make Tile class for Room.

! To counter future problems, such as:
* Colliding with tiles which're off-screen.
* Cleanly altering the collision state of a tile not yet drawn.
And so on.

In order to enforce this, there will be three modes:
* Active: drawn, collidable
* Passive: NOT drawn, collidable
* Removed: NOT drawn, NOT collidable