Add voice clips support

[diederik]

Voice clips are sound files sent over P2P (we have MsnObjectTransferP2P for this already). We love to receive this as well, and maybe send it. See ttp://www.hypothetic.org/docs/msn/phorum/read.php?f=1&i=1 for more general information.

It could be possible however that we can't play the sound files, it's said that WLM uses the closed "siren7" for it.

Stuff to do for receiving:

• change the clientcaps to announce support for voiceclips
• handle the datacast message properly.
• download the file. see if it can be played.
• implement the playing controls in the chat window.

Stuff for sending:

• be able to recond a sound file.
• announce it using the datacast message.
• send the announce, implement the invitation request in MsnObjectTransferP2P.