REL-2090: Added code to make migration from old way of representing parallactic angle mode to new way to preserve in update.
REL-2090: Found a bug in the ObsQueryFunctor relating to parallactic angle.
REL-2090: Removed PositionAngleMode, which has been superceded by adding PARALLACTIC_ANGLE to PosAngleConstraint. Additionally, found and fixed a few bugs.
REL-2090: Code cleanup and removal of no longer relevant (and confusing) comment.
Merge pull request #89 from sraaphorst/feature/REL-2090

REL-2090