Delta mush working, but caching system is preventing it from functioning.
Refactored geoemtry operators to provide a more detailed report of the attribute interactions.

Cache system now caches IO attributes before each operator is evaluated.
Renamed 'getAttributeDependencies' to 'getAttributeInteractions' to be more clear.
Fixed bugs in the caching system.

Delta mush now appears to be working.
SkinningModifier now operates on Points instead of attributes.
Tweaking demos to debug skinning issue.
added OGLFlatOverlayShader
Made 'evaluate' an io method.
delta mush working!
Fixed name change with picasso(revert this commit to be compatible with rivera(1.14))
Added better error reporting from the AlembicImporter.
Added rendering toggle to the GeometryStack
cleaned up code duplication in the DeltaMushModifier
WrapModifier working.

ModifierStack now is a Notifier and the WrapModifier a listener.
fixed bugs in debug drawing for the WrapDeformer.
fixed bug in skining export script from Maya. Normals still get broken in severe poses.
Implemented custom point normal computation to avoid bugs in existing code.

Added debugging to the NormalModfier.
minor cleanup.