Add the methods DatumElement::getBasePoint() and DatumElement::getDirection() to hide implementation details and guarantee consistent behaviour.
Using the methods fixes several regressions in:
* Constraint::getDirection
* PolarPattern::getTransformations
Most of App::Origin is moved into this sub class of App::Origin.
Add App::Point. Change graphics of the planes/axis.
Remove scale-by-content behavior and make it fixed size on screen.