KicadModTree fixes and extensions

This MR contains several fixes and extensions on the KicadModTree.

In particular the changes are:

Circle.py

• implement cutting of circles by re-using cutting of arcs (see also geometric_util.py below)

Node.py

Node.remove()got two additional arguments:

• traverse (default False) which traverses through the complete hierarchy of nodes to check if it can be found and eventually removes it
• virtual (default False) allows to also remove virtual nodes; this will make the internal node information of nodes which have virtual nodes (e.g. PolygonLines) inconsistent, but in certain circumstances this may be required (e.g., if you want to cut the basic Silk shapes by the mask layer).

For this it was convenient to implement several iterators:

• implement a default iterator Node.__iter__() to iterate through all (normal + virtual) nodes
• implement iterators Node.normalChildItems() to iterate through normal children and Node.virtualChildItems() for virtual children and Node.allChildItems() to iterate through all children (similar to Node.__iter__())

Polygon.py

• an obvious fix of an obviously never executed piece of code

PolygoneLine.py

• implement isPointInsideSelf() to check if a point is contained inside a polygon based on computing the winding number
• implement cut() to cut a polygon-line with any other geometric shape

Vector2D.py

Implementation of convenience functions:

• scalar * Vector2D (so far only Vector2D * scalar which was annoying)
• norm() and arg() to get the cartesian norm and the angle argument separately (not just via to_polar)
• inner() to calculate the inner product (aka. scalar product) of two vectors
• is_nullvec() to check if a Vector2D is (close) to the null vector
• normalize() to scale a vector by its length into a unit-vector

geometric_util.py

• implement normalize_angle() to re-project an arbitrary angle to the interval [-180, 180) degrees or [-pi, pi) radians
• fix geometricLine.isPointOnSelf which sometimes failed if the line was pointing close to 180 degrees
• fix constructor of geometricCircle.__init() to accept geometry keyword do we can easily go between Circle and geometricCircle (was only used in Circle so far)
• implement getMidPoint (to get the middle point of the contour) and isPointInsideSelf (to check if a point is inside or at the contour) for all geometric shapes
• implement geometricCircle.cut() by re-using geometricArc.cut(); the result is in both cases a list of arcs.
• extend BaseNodeIntersection.intersectTwoNodes() to handle intersection of iterable compound objects (e.g. PolygoneLine, RectLine, etc)

These changes are a preparation for !832 (merged) (the cleaned up version of !817 (closed)).

TODO:

• unittest for Node changes
• unittest for Vector2D changes
• unittest for Circle-Circle intersection
• unittest for PolygoneLine intersection extension