Scenegraph test context now returns created nodes through given table.
Working through hand-rolled bounds calcs.

There are huge problems w/ how bounds propagate right now.
1) unconditionally, node_c uses either the bounds from children or nothing.
2) nodes::shape_c always unions with the empty rect it gets from its children.

We have a sort of inversion. We need the base class to call a virtual method
in the derived class to calc the local bounds and then combine that with the
child bounds, if any.