Added divisions plug to Plane node.
Added Cube scene source.
Added Sphere scene source.
Moved Gaffer.SphereNode to GafferTest and updated test cases. Fixes #97.
Only getting plug values once during compute.
fixing silly mistake in previous commit...
Merge pull request #334 from andrewkaufman/primitiveGenerators

Primitive generators
Added a Text node to GafferScene.