Fixed buffering issues on Icecast source server and Icecast server sides

* Don't read less than meaningful amounts of data in the Icecast source
  server, just to help avconv along.
* Buffer encoded output and blast a few seconds worth to newly connected
  clients so they buffer and start playing quickly.
  (Note there's still about a 1 second delay we can eliminate because
   the blast only happens when wakeAndSendEncodedAudio() is called,
   which is not immediately upon getting a new connection.)
* Tests good for streaming playback of local files and Icecast sources
  (Mixxx).
* Tests good for no dropouts or glitches in the streaming output
  in Google Chrome, VLC, and curl.