ENH: overset: various improvements in the framework

The improvements include:

- Allowing overset patches to be displaced outside background domain.
  - The approach does not support overlapping of multiple inset meshes
    on top of background domain.
- Allowing fringe faces to walk away from hole cells in background domain.
  - The approach was not extensibly tested with overlapping patches.
- Improving mass conservation.
- Various experimental entries are removed: massFluxInterpolation, ddtCorr.
- New entries:
  - oversetAdjustPhi: adds a flux correction outside the pressure equation.
  - massCorrection: adds an implicit correction.