Shadows from windows

A PssmShadowRenderer now causes the player to cast shadows onto the
platforms. The direction is set to the same as the light from the
windows. The shadow renderer is higher-level than the level chunks, so
introducing chunk-specific light sources with new shadowing
capabilities is not supported.
Merged shadowed-windows into master-computer

This adds code for shadows cast from the windows behind the player, but
the actual shadow renderer is commented out.
Merging hazards, shadows and master-computer

This syncs a version of master.computer that had hazard-development
merged into it, with a version that had shadowed-windows instead.