Sketch splines - general overhaul

[ptc-255508]

Surface modelling was the main area which set Creo apart from the ususal suspects but they have now pretty much caught up (though the Style feature still keeps Creo ahead for ID jobs)

Workflow for editing sketched splines is looking pretty clunky, needs a general overhaul and primarily bringing into the main sketching environment rather having to enter its own interface.

[pimm]

Overall I like splines better than our other CAD system; however I do not like how it forgets it's original intersection if you apply a corner radius.  It wants to convert the construction geometry to a line instead of the original spline.  This can end up really distorting the result if changes are necessary.