and some further minor jingle fixes:
- deprecate getJingleTransport() in favor of getTransport()
- Jingle.Builder now checks if the session ID is not empty
A start for the new Jingle API. Since Jingle is a single IQ with many
plugable extensions, there are some particularities we need to deal
with, e.g. jingle users have to register with JingleManager.
This is untested code. There may be drangons.