* Enforce fixed column number at various width breakpoints.
* Bring back the filmstrip at small sizes but hide it.
* Change default maximum columns to 7.

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

* Implement opening toolbar and participant overflows as drawers when below certain width.
* Fix dial-in copy button displaying incorrectly.

Co-authored-by: Saúl Ibarra Corretgé <saghul@jitsi.org>

Due to how the filmstrip size if computed I don't think there is a good way to
animate the change in size, so just ignore the toolbar, it will be hidden soon
enough.

- Lower the inter-tile margin to 2px
- Remove the 100px top/bottom margin when the toolbar is hidden

* feat: Drops filmStripOnly mode.

* squash: Let's make lint happy again.

* squash: Drop some css.

Co-authored-by: Saúl Ibarra Corretgé <saghul@jitsi.org>

Makes the tiles consistent as the participant view is equally sized and the
avatar is always centered in the tile.

Moves the logic from all different places into single state
listener to combine all inputs into a single output.

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.

Use a dimensions detecting root component. The Dimensions module does not
measure the app's view size, but the Window, which may not be the same, for
example on iOS when PiP is used.

Also refactor the aspect ratio wrap component since it can be taken directly
from the store.

Last, remove the use of DimensionsDetector on LargeVideo and TileView since they
occupy the full-screen anyway.

Fixes PiP mode on iOS.

When the reccorder joins, they have a local participant, which is not rendered,
so don't count it towards the partcipant count used for computing the tile
sizes.

Regresssion from bd8a7edbd2.

When the toolbar buttons are overridden with URL parameters, our computed set of
buttons will be wrong. Thus, compute it every time and check for the
differences.

Note that in the usual (vertical) setup, the "toolbar" is just the hide button.

* fix(thumbnail): Optimize status bar moderator icon

Moved all moderator functionality to react to optimize the number of
status bar updates.

* fix(RemoteVideoMenuTriggerButton): Use nullish coalescing

Co-Authored-By: Saúl Ibarra Corretgé <saghul@jitsi.org>

* ref(StatusBar): rename to StatusIndicators

* fix(RemoteVideoMenu): isModerator value.

* fix(notification): mobile.

Co-authored-by: Saúl Ibarra Corretgé <s@saghul.net>

Since the verical filmstrip doesn't set its width explicitly anymore,
calculating the available area for the large video based on the
filmstrip width retrieved from the HTML element was wrong
in the cases when the rendering and cleanup of the filmstrip hasn't
finish yet. For example when switching from tile view to stage view.

* ref(Filmstrip): Optimize resizes.

* fix(thumbnails): resize.

* fix(thumbnails): Issue with height 0, width 0.

* doc(Filmstrip): Improve JSDoc.

Simplifies the code a bit, and we use no lifecycle methods.

Audio streams are automatically played by WebRTC and this won't change, probably
ever. There is no point in having checks and an Audio component which does
nothing.