Bez Curve mockup using bSpline tools.

Add Edit functionality to mockup
fix Close button for BexCurve Edit
fix tracker behaviour in for BezCurve.undoLast
Draft beziers: Split poles to multiple bezier segments

Draft set degree of bezier curve
Close Draft bezier curves
implement addPoint for piecewise Bezier curves
use circle trackers for control points
prepare functions to make bezier knots tangent or symmetric
make Draft.BezCurve nodes tangent/symmetric
instead of moving both poles to the same side, we make them symmetric

changed icon Draft_BezTanNode
fix DWire,BSpline, BezCurve edit buttons

fix bug in Draft.Edit re incorrect tan/sym on DWire/BSpline
update Draft_rc for new Draft_BezTanNode.svg
Draft: Enhancements in Bezier Curve Editor

Draft move poles with knots for Bezier Curves with Degree >=3
Draft: make bezier curves symmetric/tangent when clicking on poles
Draft Bezier Curve: implemented Continuity Property