ENH: improve robustness of scalarRanges from string (fixes #673)

- now avoid Istream and token mechanism in favour of a simpler string
  parser. This makes the code clearer, smaller, robuster.

- provide convenience ge/gt/le/lt static constructors for scalarRange
  for using bounds directly with specifying via a string parameter.

- scalarRange, scalarRanges now follow the unary predicate pattern
  (using an operator() for testing). This allows their reuse in
  other contexts. Eg, for filtering operations:

      myHash.filterValues(scalarRange::ge(100));

- remove unused scalarRanges methods that were specific to handling
  lists of time values. These were superseded by timeSelector methods
  several versions ago.

etc/controlDict

@@ -813,7 +813,6 @@ DebugSwitches
     saturateEvaporationModel 0;
     scalarAverageField  0;
     scalarField         0;
-    scalarRange         0;
     scaleSimilarity     0;
     scatterModel        0;
     searchableBox       0;