Remove MSNXMPP specific code

The MSN XMPP gateway was shutdown december 2013 and isn't coming back.
Handle not-authorized stream errors, avoid reconnect

Got this one while trying to connect to google servers with hipchat auth
Add support for XEP-0203: Delayed delivery (message timestamps)

Very similar to XEP-0091 which is already supported, but was marked as
obsolete, replaced by XEP-0203. The main differences are the tag name
and the timestamp format.

Due to the similarities, both XEPs are still supported.