msrpstream: add MSRPOutgoingFileStream and MSRPIncomingFileStream

- remove sounds from MSRPChat
- don't use callFromAnyThread or spawn_from_thread - we usable only in twisted thread
- make MSRPChat.__init__ accept direction and file_selector as optional params
- store MSRPSession under 'session' attribute and MSRPTransport under 'msrp'
- do not depend on green.sessionold module
- add MSRPChat._on_start() method to be overriden in subclasses

darcs-hash:20090421074552-b2873-19158cb6b0878864d7e7cf049ebbbf06bfdfa929
sip_session2: early support for sendind/receiving files

- to send a file, type :send URI filename
- or from command-line, ./sip_session2.py URI filename

darcs-hash:20090421074608-b2873-dcaac07a493dec5a8586700cf7bffa7c78646e81