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.

* Add participantRoleChanged event to external API

* Update API documentation

* Remove unneeded whitespace

* Remove more unneeded whitespace

* Fix jsdoc formatting

* Fix jsdoc formatting

Fixes: https://github.com/jitsi/jitsi-meet/issues/4049

* ref(feedback): emit api feedback submitted on completion

Compared to firing the event on submission because
the submission ajax will not be completed at that
time..

* squash: update package.json

- Use actions to notify the rest of the app that
  a mic or camera error has occurred
- Use middleware to respond to those notifications
  of errors by showing in-app notifications and
  notifying the external api