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.

* Prints errors in case of wrong initialization.

Not printing can masks some errors in the code.

* Allow only one Follow Me moderator in a meeting.

* Sends Follow Me state with all presences of the moderator.

This fixes an issue where the moderator sends the Follow Me state and then for example mute or unmute video (this will produce a presence without Follow Me state) and the new comers will not reflect current Follow Me state till a change of it comes.

* Changes fixing comments.

* Changes fixing comments.

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