Clean up ModuleIdentifier use in yang-parser-impl

YANG parser's use of ModuleIdentifier is muddling its definition, because it is using weird wildcards to express import/belongs to statements – specifically it is using constants to express 'no revision'.

These should be handled via a ModuleIdentifier matcher class, so that the wildcard match is correctly expressed and we can eliminate SimpleDateFormatUtil's DEFAULT_DATE_REV, DEFAULT_DATE_IMP and DEFAULT_BELONGS_TO_DATE.