Audio AAC compression

Hello,

This is the first time I contribute to GitHub, I hope I'm doing it right :)

Please review my "Pull Request", I have done the following:
1. Audio recorder now records to a compressed AAC format rather than raw uncompressed PCM 
2. So basically a mono recording of 1 minute at 64k kb/s will add ±480 kilo-bytes to the mov file, down from ±5 Mega-Bytes in PCM.
3. I made the following changes:
    A. Audio recording is now "On" by default (As the audio takes an order of ±10 times less than before)
    B. I believe the use case of this App would benefit more from a Mono being the default rather than Stereo
    C. Always record at the (hardware) preferred  44100 samples per second to provide the AAC encoder with the best "material" to work with (and avoid hardware level down-sampling)
    C. Let the user choose the AAC bitrate  (32kb/s, 64kb/s, 96kb/s and 128kb/s). Given that mp4/AAC 128kb/s is equivalent to an mp3 file with a bit-rate of 192kb/s, it should be a good upper-limit.
4. The recorder object will get and keep the "Should record audio?" boolean at "start". In case it is set to "No", the microphone will not be opened, and an audio file will not be mixed in.

Happy new year :D
-Doron Adler