- old 'DELETE' enum was easily confused with 'REMOVE', which removes
the set, not the elements from the set.
- provide corresponding subtractSet() method
STYLE: HashSet set/unset instead of insert/erase methods in topoSetSource
- simplifies switching to/from bitSet storage
Update of overRhoPimpleDyMFoam and overInterDyMFoam solvers.
Adding corresponding tutorials with best possible settings
The main effort was put on reducing pressure spikes as the
stencil change with hole cells on the background mesh.