* Unify chat open/close size changes and move them to redux.
* Fix responsive columns not accounting for chat.

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

* 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

Follows me and switching to tile view, still works.

* feat: Drops filmStripOnly mode.

* squash: Let's make lint happy again.

* squash: Drop some css.

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

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

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.

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.

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.

Any overrides set on interfaceConfig are not
applied on module load. As such, call to get
the value of the auto pin setting, providing
time for the bootstrapping to set overrides.
Otherwise iframe api users cannot override
the setting.

React Native doesn't define __filename nor __dirname so do it artisanally. In
addition, this helps with centralizing the configuration passed to loggers.

The store's remote tracks get cleared
and re-added when switching in and out
of p2p, which can cause pinning thrashing.
Avoid that with a debounce.

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

🔥🔥🔥

Using anything non-serializable for action types is discouraged:
https://redux.js.org/faq/actions#actions

In fact, this is the Flow definition for dispatching actions:

declare export type DispatchAPI<A> = (action: A) => A;
declare export type Dispatch<A: { type: $Subtype<string> }> = DispatchAPI<A>;

Note how the `type` field is defined as a subtype of string, which Symbol isn’t.

- Reset some state on the singletons conference
  and VideoLayout.
- Add a way for LocalVideo to clean itself up
  by sharing logic with the other SmallVideos.
- Add clearing of chat messages so they don't
  linger.
- Remove some UI event listeners.