Port shadow shaders to singleton and remove non singleton.
Port stkbillboard to singleton shader
Fix ambient term.
clean up billboard text code
Enable ref + vertex color for unlit mat.
Text billboard uses unlit material.
Merge remote-tracking branch 'origin/master' into bumpy
Support vertex color for alpha ref material.
Fix shadows for unlit with alpha ref.
Merge remote-tracking branch 'origin/master' into bumpy
Use singletonshader template for colorize
Add a static assert.

Check if we pass correct count of uniforms name to AssignUniforms().
Better if we dont remove the real function call...
Forget the ...
Disable depth test in non dynamic light mode.

Just in case...
Merge remote-tracking branch 'origin/master' into bumpy
Removed support for non-bevelled shapes (has not been used in years).
Fixed position of physical (raycast) wheels to be in (or on the edge)
of the collision body, not outside. Removed support for defining
kart-specific physical kart position (was never used).
Increase impulse to keep the kart parallel (to avoid the kart being
90 degrees on its side and not being able to get straight again).
Increased impule to keep kart parallel a bit more, changed the bevel shape
to be slighlty longer.