ENH: consolidate handling of mandatory/optional command arguments

- for some special cases we wish to mark command-line arguments as
  being optional, in order to do our own treatment. For example,
  when an arbitrary number of arguments should be allowed.

  Now tag this situation with argList::noMandatoryArgs().
  The argList::argsMandatory() query can then be used in any further
  logic, including the standard default argument checking.

- with the new default check, can consolidate the special-purpose

      "setRootCaseNonMandatoryArgs.H"

  into the regular

      "setRootCase.H"

- revert to a simple "setRootCase.H" and move all the listing related
  bits to a "setRootCaseLists.H" file. This leaves the information
  available for solvers, or whoever else wishes, without being
  introduced everywhere.

- add include guards and scoping to the listing files and rename to
  something less generic.

     listOptions.H -> setRootCaseListOptions.H
     listOutput.H  -> setRootCaseListOutput.H