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.

These provide the ability to integrate the SDK with some other application
loggers.

At the time this was written we use Timber on Android and CocoaLumberjack on iOS.

In addition to the integration capabilities, a LogBridge React Native module
provides log transports for JavaScript code, thus centralizing all logs on the
native loggers.

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

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.

The logMessage can be very long. Probably only it's length could be
important to why sendApplicationLog has failed. Stringify the error
though.

Stores the Logger.LogCollector instance in base/logging state instead of
global APP variable and enables it on mobile.

BaseApp does all the heavy-lifting related to creating the redux store,
navigation, and so on.

App currently handles URL props and actually triggering navigation based on
them.

In order to be able to add analytics to the deep-linking pages the
lib-jitsi-meet initialization has been moved so it happens earlier.

The introduced `initPromise` will eventually disappear, once conference is
migrated into React and / or support for Temasys is dropped. At that stage, it
can be turned into a sync function which all platforms share.

* Adds in memory log storage, to be used while testing.

Enabling it only when config.debug is set, a configuration provided by jitsi-meet-torture.

* Moves to using config.testing.testMode property for logs storage.

* Fixes comments.

When _setLoggingConfig is invoked for the first time old and new config
are equal and _initLogging is not called. Currently, there is no way to
detect when the first time we call it is. We could use APP.logCollector
but it should go away at some point in the future.

The counterpart of the external API in the Jitsi Meet Web app uses the
search URL param jwt to heuristically detect that the Web app is very
likely embedded (as an iframe) and, consequently, needs to forcefully
enable itself. It was looking at whether there was a JSON Web Token
(JWT) but that logic got broken when the JWT support was rewritten
because the check started happening before the search URL param jwt was
parsed.

The functionality around logging including logging_config.js i.e.
loggingConfig and the other classes and/or functions that initialize
loggers for Jits Meet truly deserves a feature of its own. Start getting
in that direction on both Web and mobile by introducing
features/base/logging and bringing loggingConfig to mobile.