fix scene template (remove draw funcs, add fixed-/update, impl scene root)

!!! document input code, document hierachical transforms

make a sample implementation of the ai module, remove the ai enemy grunt file afterwards.

clean up utils

figure out how to do depth sorting / draw sorting

• figure out how to determine what objects are rendered for what render stage
• how do render stages interfere with depth sorted rendering?
  • each stage could have it's own depth buffer, and at the end they are composited using the depth buffer