Speech recognition related

A little hacking based on `avTouch` project:

1. Use `AVAudioRecorder` instead of cpp implementation.
2. Transplant the `libflac` for `.caf` => `.flac` convertion.
3. Use `AFNetworking` to upload and invoke google speech api. 
4. Show level meter for recorder other than player
5. Auto detect silence to stop recording.

Happy Hacking && Happy New Year !!

@mockee @Sunight