Make toolbar's microphone button enabled whenever there are any
'audioinput' devices available and allow to add audio during
the conference even if microphone permissions were denied on startup.

Dynamically enables/disables the toolbar video button. Prior to that
commit if we would start with no video there would be no way to enable
it later on.

toolbox/functions has functions that are specific only to web,
specifically defaultToolbarButtons. This has caused the native
build to attempt to bring in a web dependency which leads to a
build error. The fix for now is splitting web functions from
native functions to resolve the build error.

Saúl Ibarra Corretgé reported that Recording shows an error dialog
stating "There was an error connecting to your camera". Hristo Terezov
and Yana Stamcheva traced that the problem originates in
da4425b5c0
and, more specifically, is caused by a different order of execution due
to the move of the invocation of the function Recording.init.

The solution is to bring back the execution location of Recording.init.

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.