refs #10019. Extend V3D and test
refs #10019. Expose methods to python and test
refs #10019. Remove ExtendedUnitCell class
refs #10019. Minor modifications.
refs #10019. More helpful about python arguments.

Following Andrei's suggestion. Internally convert to V3D from other types. I've also enabled the default choice of inDegrees for the V3D::directionAngles from the python side. All changes are unit tested.
Merge remote-tracking branch 'origin/feature/10019_direction_angles'