Also unify the mobile and web features into one, even though internally they still have separate ways to enable the functionality.

Introduces a new feature flag ('help.enabled') and uses that to
determine the visibility of the 'Help' button in a call.

Features flags added:  
-tile-view.enabled
-filmstrip.enabled
-notifications.enabled
-toolbox.enabled

Also, use the configured resolution to set it as the max received frame size.

Android for Enterprise provides special feature for applications to obtain configuration through RestrictionManager remotely by some MDM solution.

Jitsi Meet can be remotely installed and provisioned with a proper URL (making URL not editable by the user) inside the Work Profile or Fully managed device.

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.

- Invite funcionality (altogether)
- Recording
- Live streaming
- Meeting name
- Meeting password

Currently only 2 options are implemented, mainly aimed at helping troubleshoot
audio related problems:

- Disable native call integration (it disables CallKit / ConnectionService)
- Disable P2P

The welcomePageEnabled and pictureInPictureEnabled props on mobile have been
converted to feature flags.