Parser should be less verbose when logging debug messages

When logger level is set to DEBUG and parsing yang file, YangParserListenerImpl produces large amount of messages like

16:37:12.335 [main] DEBUG o.o.y.y.p.i.YangParserListenerImpl - entering extension required-identity (40)
16:37:12.335 [main] DEBUG o.o.y.y.p.i.YangParserListenerImpl - exiting extension required-identity

It might be better to move those messages to TRACE level.