make audio processing constraints configurable (#491)
make audio processing constraints configurable (#491)

* make audio processing constraints configurable

AP: echoCancellation is a "master switch" for disabling all audio processing.  set to disableAP=true and stereo=true allows fullband, stereo sound.
AGC: misbehaves with certain 'pre-gained' mics.
HPF: can't hear any effect but it's the last constraint to make configurable.

* Update RTCUtils.js

damencho/lib-jitsi-meet,nevermind-corp/ljm,jiyeyuran/lib-jitsi-meet,jitsi/lib-jitsi-meet,adambowles/lib-jitsi-meet,jitsi/lib-jitsi-meet,adambowles/lib-jitsi-meet