Add fancy unit/math input to pad tool

Pad tool does not currently save the units, so the result is still in mm.
Merge remote-tracking branch 'refs/remotes/s7726-repo/PadToolDatum'
Fully implement Units in PartDesign Pad
Avoid OCC error for closed Draft.BSpline with same first/last points
Merge branch 'master' of ssh://git.code.sf.net/p/free-cad/code