The behavior can be triggered with the toggleAudioOnly action, which is
currently fired with a button.

The following aspects of the conference will change when in audio only mode:

- local video is muted
- last N is set to 0 (effectively muting remote video)
- full-screen mode is exited
- audio mode is set to "audio chat" (default output is the earpiece)
- the wake lock is disengaged

One aspect not handled in this patch is disabling the video mute button while in
audio only mode. The user should not be able to turn back video on in that case.

When a new local video track is created an associated video capturer is created
for it. The cause for the freezes seems to be creating mutliple tracks (which
come with a video capturer each). Fix this by first disposing of the previous
video track before creating the new one.

Ref:
https://github.com/oney/react-native-webrtc/issues/209#issuecomment-281482869

It got broken while rewriting the Web toolbar in React Toolbox. There is
a problem with the toolbars and how we construct the intialState of the
buttons. The _getInitialState() in the toolbox reducer gets the list of
buttons from interfaceConfig, but in fact interfaceConfig is meant to be
overriden in several very important cases. One of the cases being the
external API, which we use in several projects in production.