One more construction path for SimpleShapeletMatrixBuilder

If we pass a sufficiently simple MultiShapeletBasis to
a MatrixBuilderFactory (as we will when fitting PSFs to shapelets), we can use this implementation.
Start implementing CompoundMatrixBuilder
Add RemappedShapeletMatrixBuilder
Add copy-ctor, increment method to Workspace; remove assignment
Make it possible to pass ellipses to testing utility functions
Finish implemention for non-convolved CompoundMatrixBuilder