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.