LCM: Numerous changes:
- Topology modification seems to be working.
- Checking interface to mechanics reveals chicken-egg problem between
the Topology and FractureCriterion classes.
- Refactor these classes so that FractureCriterion is as minimal as
possible and relocate most if its data and some of its functionality to
Topology.
- Propagate these changes all over.
- Because debugging is sometimes rebugging, things don't quite work as
expected yet after these changes. Working on fixing this.