WIP: Internal pipeline+appsink approach

- based on AudioStreamChannelReader impl
- AudioStreamChannelsReader has been kept in a separate
  C++ class for now..
- Added 'query' function to webkitWebAudioSrc element, mainly
  to provide 'latency' information required by sink element to
  synchronization stuff

WIP: currently working only in loopback, skiping webkit's webaudio
    stuff :)

FIXME: It's still getting underflow warnings in pulsesink

Signed-off-by: Nick Diego Yamane <nick.yamane@openbossa.org>