Properly apply custom materials with CanvasGroups in the GLES3 backend
Properly blur backbuffer when using a partial rect in forward_plus and
gl_compatibility renderers
Properly set fit_margin when clear_margin is set
Fix shader error during backbuffer clear in mobile renderer
This allows light sources to be specified in physical light units in addition to the regular energy multiplier. In order to avoid loss of precision at high values, brightness values are premultiplied by an exposure normalization value.
In support of Physical Light Units this PR also renames CameraEffects to CameraAttributes.
