ENH: add isTrue function to RunFunctions

- check if the first argument corresponds to an OpenFOAM value for
  'true' (as per Switch).
  True == 't', 'y', 'true', 'yes', 'on'. Everything else is not true.

- when the first argument is '-dict', it initializes the value
  with a query via foamDictionary.
  Eg,
       isTrue -dict mydict -entry parallel

   ==> value=$(foamDictionary mydict -entry parallel -value)
       isTrue $value

   a missing entry is silently treated as false.

ENH: add getNumberOfPatchFaces function in RunFunctions

- simple extraction of nFaces from boundary file for given patch/region