ENH: use updated globalIndex methods

- range(proci) instead of localStart(proci), localSize(proci) combination.
  * does the same thing, can be used directly with various other
    routines for slicing etc.

    Eg,
       Foam::identity(globalNumbering.range(myProci))

- globalIndex::calcOffset() instead of constructing a globalIndex and
  taking the localStart(). Avoids intermediate resizing and storing of
  an offsets table (which is then discarded) as well as the subsequent
  lookup into that table