def supports_currency_types_for_conversion(self, source_currency_type=None, target_currency_type=None):
Tests if a given currency conversion is supported.

        arg:    source_currency_type (osid.type.Type): the type of the
                source currency
        arg:    target_currency_type (osid.type.Type): the type of the
                target currency
        return: (boolean) - ``true`` if the given source and target
                conversion is supported, ``false`` otherwise
        raise:  NullArgument - ``source_currency_type`` or
                ``target_currency_type`` is ``null``
        *compliance: mandatory -- This method must be implemented.*