Remove unused ClosestPatchEnd method
Add log_slider flag to AddSlider
Add STEP export option parameters to Vehicle
Add STEP Options screen to GUI framework
Show STEP Options screen before FileChooser when exporting STEP files.
Pass STEP options through to writing surfaces.  Don't take action yet.
Optionally use PntNodeMerge to make STEP surface export re-use repeated control points.
Make VspSurf STEP output work on vector of surfaces.

No functional change here, mostly just changing indentation.
Change VspSurf::SplitSurfs to not assume start from m_Surface
Optionally split surfaces for STEP export.
Optionally force surfaces to cubic in STEP export.
Change the way surface orientation is controlled for STEP export.
Change STEP export default to merge coincident points.