Merge pull request #2520 from RosettaCommons/vmullig/refactor_crosslinkermover
Refactor the CrosslinkerMover a bit for generality
Needed for planned work with metals and for other crosslinkers. Ideally, this should cause no test changes, beyond minor cosmetic changes due to a changed input.
Tasks:
- [x] Update documentation ("threefold_symmetric" option is now "symmetry").