Add piecewise patch getters that return parameter specs for patch too.
Fix piecewise surface parameter_report.

Was changed to const method without changing to use a const iterator.
Add single-segment append to piecewise surface parameter_key.
Add piecewise surface private method for extracting a part of a surface
Add piecewise surface split_u/v methods that return subsurfaces
Add tests for piecewise subsurface splitting routines.
Merge branch 'feature/SubSurfaceSplit' into develop