FIX: Fix and reorganize examples

@almarklein mentioned that we should get all our examples working. Toward that end, I made a bunch of changes, some of which were necessary to make examples run on my system (OSX, picky GLSL compiler).

Here are the examples that still don't work for me -- can anyone else take a stab at fixing them?

Almar:
glsl-sandbox-cube.py (doesn't update)
howto/split-screen.py (doesn't display anything)

Luke:
scene/*
modular_shaders/sandbox.py (error)

Deleted:
techniques/grid/*