ENH: support format readOptions for surfaceReader types (#2609)

- similar to surface writing formats, also support optional
  dictionary of reading options. The main beneficiary of this is the
  ensight surface reader:

  readOptions
  {
      ensight
      {
          masterOnly true;
      }
  }

  This will restrict reading to the master rank. Surfaces and values
  read will be broadcast to the other ranks, with the intention of
  reducing load on the filesystem.

ENH: add writing of Dimensioned fields for areaWrite functionObject

- can be useful for examining finite-area source terms