Move primitive.CurveSegment to coordinate package

The inheritance hierarchy is

coordinate.GenericCurve
/|\
primitive.CurveSegment
/|\
coordinate.*

that is both the parent and all the children of the CurveSegment are in coordinate. Therefore, CurveSegment should be as well.

The split happens because GenericCurve has children in both packages but it must live in one. However, CurveSegment is clearly in the wrong place.

Solution is to make a new coordinate.CurveSegment interface with the contents of the current class and change the current class to be a shell which simply extends the new interface and is deprecated.