This PR introduces the new PlaneBase class.
Most of its functions are rewritten versions of the functions in the original Plane class, with the exception of align_to_point_and_axis_svg.
Note that after this PR the original Plane class does not yet inherit from PlaneBase. This will be done in several following PRs. I will then also explain the reasons behind some of the revised functions in PlaneBase.
The introduction of the PlaneGui class will follow after that.
Issue: #5603.