Use subscribers to detect state change and emit those
out to other participants. Use middleware to register
the command listener.

This reverts commit 9625be1db3.

The Audio.js setRef callback does not behave like react ref callback
in that the former will not have fired before componentDidMount
but the later will have. So for audio output preview, trying to set
sink id on mount will no-op because it does not have a ref yet to
Audio.js, possibly leading to audio output previews playing on
the default speaker device. This generally has not been a user
visible problem due to coincidence; other re-renders necessary
by the parent of audio output preview will have triggered
componentDidUpdates on the audio out preview, which would then
set the sink id on the Audio.js ref it should have received
by then.

Searching for a device (id) by label alone can result in
false results when devices share labels, such as a mic
and speaker having the same label. To prevent such,
specify the device kind to be found instead of iterating
over all device kinds.

When the iFrame api is used to set a preferred audio output using
options passed into the JitsiMeetExternalAPI constructor, no logic
fires to actually change the audio output destination.

Devices of different kinds can have the same id, such as speaker
and mic both being default. Using id only can then lead to
incorrectly setting device descriptions in the current devices
object.

If tracks are created while the conference is in the 'joining' state
they will never be added.

* ref(display-name): do not pass in display name

The component gets the state itself from redux.

* fix(display-name): do not default name to placeholder name

The web display name component supports inline editing of
the name. Problems can occur when the displayed name
differs from the actual saved name, because participants
without a display name, including the local user, have
a different, default display name displayed. So when
editing starts, the input field is populated with the
default name. To workaround such while supporting fetching
the display name using mapStateToProps, pass in both the
name which should be shown and the name value saved in
settings.

* ref(display-name): rename methods

Only one notification will be displayed at a time on mobile.

Adds 1 liner notifications to mobile. Only the title is displayed. In
case the title is missing there's a fallback to the description.