Up until now we relied on implicit loading of middlewares and reducers, through
having imports in each feature's index.js.

This leads to many complex import cycles which result in (sometimes) hard to fix
bugs in addition to (often) breaking mobile because a web-only feature gets
imported on mobile too, thanks to the implicit loading.

This PR changes that to make the process explicit. Both middlewares and reducers
are imported in a single place, the app entrypoint. They have been divided into
3 categories: any, web and native, which represent each of the platforms
  respectively.

Ideally no feature should have an index.js exporting actions, action types and
components, but that's a larger ordeal, so this is just the first step in
getting there. In order to both set example and avoid large cycles the app
feature has been refactored to not have an idex.js itself.

Moves the statsEmitter.start() invocation to the middleware of
the connection-indicator feature, so that it's started for both mobile
and web (now mobile needs RTP stats for the tests).

Instead of passing stats through UI then VideoLayout then the
SmallVideo, pass stats directly to what uses it--ConnectionIndicator.
This also bypasses adding the stats to the store, as they do not
seem to be something that needs to be shared or stored app-wide
just yet.

- Create a new ConnectionIndicator component for displaying an
  icon for connection quality and for triggering a popover. The
  popover handling has been left in ConnectionIndicator for now,
  which follows the existing implementation.
- Remove the unused method "connectionIndicatorShowMore"
- Change the implementation of existing methods that update the
  connection indicator to call the same method which will rerender
  the indicator completely.

Move all logic related to displaying a table of connection stats to a React
Component. The actual parsing logic was modified as little as possible as the
focus is moving display to React.

When callstats is not configured hide the button.

As an intermediate step on the path to merging jitsi-meet and
jitsi-meet-react, import the whole source code of jitsi-meet-react as it
stands at
2f23d98424
i.e. the lastest master at the time of this import. No modifications are
applied to the imported source code in order to preserve a complete
snapshot of it in the repository of jitsi-meet and, thus, facilitate
comparison later on. Consequently, the source code of jitsi-meet and/or
jitsi-meet-react may not work. For example, jitsi-meet's jshint may be
unable to parse jitsi-meet-react's source code.