Change constants to numeric values.
Change constants to numeric values.

 - This should have been done in a previous commit.
   Now we are using luigi to parse the config files,
   we don't have a hook to convert numeric values
   (expected in by matlab) to strings (as was being
   expected by PyRate). Hence we need to stick to
   The numeric values. It was not obvious that this
   was needed for any reason.

GeoscienceAustralia/PyRate,GeoscienceAustralia/PyRate