Preliminary. Does not work.
unworking stage to change branch
Preliminary version with ellipse represented

- No Tangency constraint
- No point on Ellipse curve constraint
- No radius constraint
- No X axis to ellipse major axis angle constraint
- No real interative creation
Ellipse introduction button via (center,majaxis extreme, a point in edge)
- Some initial ellipse implementation

- Ellipse Major and Minor Radius constraints: Initial working version (no movable yet)
Implementation of Phi angle constraint.

Corrected AngleXU direction in GeomEllipse
- Backwards compatibility with files of previous versions not defining a phi angle
- Art by Jim
- Moving constraints: Radii and EllipseAngleXU constraint

Ellipse AngleXU, with respect to line, still unimplemented
- Added limitation on entering radius a>=b
- phi constraint is not a signed value (can be -30 degrees)
Jim's arts is now in...
Major fix: Phi definition and Ellipse creation method

Initially the ellipse creation method did not attempt to control whether the user generated a CCW or CW ellipse.

Therefore the ellipse's reference system Z axis sometimes was the opposite of the Z axis of the sketch, which ultimately
led to inconsistent definition of phi, as it was measured with respect to -X (the corresponding X of a right-handed coordinate system with Z in the -Z direction).

Now all the ellipses created by the sketcher are CCW ellipses so that phi is consistent with what the user expects (from where the camera is).

This should fix most problems and inconsistencies with major and minor radii (but yes sometimes still complains that Major<Minor even if not true, this is a separate bug).
Property editor support for EllipseAngle (phi) and Radii
Element Widget support for ellipses
Fixing bug in minor radius constraint definition
Auto-resize of Major/Minor when setting a Minor/Major constraint that would lead to MajorAxis<MinorAxis

=> Resizes the non-to-be-constrain magnitude to be equal to the value entered for the to-be-constraint magnitude resulting in a circle.
=> Only if there is not any constraint on the non-to-be-constrain magnitude
=> This resize can not be undo.
Now an ellipse can be drag to another position
Fix crashing on dragging ellipse edge

Equal constraint implemented.
- Jim's Ellipse XPM. Thanks Jim!!
- Box selection for ellipses
Point on Ellipse Curve
Tangent: Ellipse to Line
Debug code with conditional compilation for gradient system matrix