The SketchPlane expects the first element to be a planar face/edge to
define a work plane for any following draft wire/circle/arc elements.
The 2D constrainted elements can either be inside the defining
SketchPlane constraint, or other constrains following the SketchPlane
in the constraint group.
Add a new SketchPlane to define a new work plane for any following
draft elements. Add an empty SketchPlane to undefine the work plane,
effectively making any following draft elements free in 3D space.
* Draft wire points can be dragged individually.
* Draft wire individual edge can be moved and rotated.
* Draft circle/arc can be moved and rotated by dragging edge or face.
* Draft circle/arc radius can be changed by dragging vertex
* Draft arc first/last angle can be changed by dragging end points
