disable AGC / Android API flags

[dpocock]

There are some optional API flags to disable AGC. It would be helpful to have a toggle button in the settings for this.

These are useful for people who want to record the audio with the app and then process the audio on a computer.

MediaRecorder.AudioSource flag VOICE_RECOGNITION disables AGC

A similar feature that disables all processing is UNPROCESSED

There are examples here:

https://stackoverflow.com/a/42239370

Here is an example of the same change in another app:

https://github.com/Kaljurand/Diktofon/pull/26/files