jabber.py 1.7: update for Python 3

* Use _sslObj instead of _sock for socket fd
* utf-8 encoding/decoding fixes
* Add __str__ method for Buddy class to return jid of buddy
* Support /whois, /query and /msg commands for jabber buddies
* Implement /away command for jabber servers
* Add XEP-0224 call attention (/jattn) command

TODO:
* use disco to check if other party has call attention enabled

Author: aelmahmoudy