Add more modes to the vad sens detection

[jnr4817]

There are 3 modes of sens detection located here:
WebRtcVadSharp/WebRtcVad/webrtc/common_audio/vad/vad_core.c

Anyway to add more. Using this code for VOX within a flight simulator and it is still to sensitive.

[ladenedge]

There are four modes available in the library using the OperatingMode enum, but you're right that they aren't as different as one might want.

It's an interesting idea to allow more variability over the constants defined by those modes. I will look into it.

[jnr4817]

Thank you