ENH: Updates to applyBoundaryLayer utility

Old:
- Previous versions created k and epsilon fields by default, and
  then processed omega and nuTilda fields if present.
- Depending on the choice of turbulence model, not all of these fields
  would be used, and could lead to errors when running some utilities
  due to erroneous values.
- If the omega field did not exist, it would be derived from the epsilon
  field, and also inherit the epsilon boundary conditions (wall
  functions)

New:
- This version will only update fields that already exist on file, i.e.
  will not generate any new fields, and will preserve the boundary
  conditions