[gufrvhcs] Maze with graffiti

A large maze from first person perspective is hard to navigate because all the twisty passages look alike.  Mitigate this by allowing players to draw on the walls.  This could also be done in real life.  Pretty soon, especially if multiplayer, there will be landmarks everywhere.

Monetize in game: paint costs money.  Or you can buy a protective coating for a section you want to preserve (it doesn't have to have been drawn by you).  Painting over a protected portion costs in proportion to the thickness of the protective coating it has.  Good landmarks are likely to stay, which is useful for navigation.

We would like mechanisms to prevent similar landmarks from being drawn in different places, though maybe the normal process of graffiti will take care of that.  Even if something starts looking similar to something else, it probably won't stay that way.

Previously (1) and (2).