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.

Update userSelectedAudioOutputDeviceId and userSelectedAudioOutputDeviceLabel when a new speaker is selected from the audio settings popup menu

Pass the real deviceId to gUM instead of 'default' for Chrome to return the correct media stream

* Add a checkbox for skipping the prejoin page on next use. (This is hidden for
now, until we also have a settings entry for it).
* Rework 'Join by Phone' buttons and add new overlay.
* Update the device status accordingly if there were errors while adding
devices.
* The input is filled with the display name if there was one previously used.
* Join the meeting on 'Enter' press.

This reverts commit faf24ca7ec.

This reverts commit 08f55ccb94.

Logs the device list when is updated in the reducer and removes
"button enabled" logging which used to dump the device list, but
in a useless way(Object[Object]).

Makes an attempt to log currently selected device, but because of
multiple possible paths it's impossible to find one reliable spot to log
selected device. One has to rely on device list and the GUM call logged
to figure things out.

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

- 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

* Groups devices notifications by type audio/video.

* Fixes passing correct device array.

Currently devices set through the api are stored
as ids, and not user selected. This can cause
other existing user selected devices to take
precedence over the devices passed into the api.

* Skips setting undefined device id to sink in audio preview.

* Fallbacks to use labels for user selected devices.

* Fixes comment.

* Fix detecting preferred audio output.

Fixes detecting when a new output device is found and we have stored user preference of using that device.

* Does not store which is the currently open device on save.

Does not save the currently opened device when saving settings dialog, this will be done once we successfully replace the tracks to use the new devices.

* Saves opened audio device after successfully changing it.

If we do it earlier _updateAudioDeviceId is using localAudio and can store wrong value.

* Adds notification for new non preferred devices.

A notification is shown which gives an option to the user to select and use the newly plugged devices.
Adding custom button and handler for the action to the notifications.

* Changes logic to search and handle all newly added devices from array.

* Moves some utility methods to features/base/devices.

The state about currently opened devices is filtered and not stored, where we only store when user selects a device preferences.
Also allow changing input devices for Firefox when we are not in a conference.

Searching for a device (id) by label alone can result in
false results when devices share labels, such as a mic
and speaker having the same label. To prevent such,
specify the device kind to be found instead of iterating
over all device kinds.

When the iFrame api is used to set a preferred audio output using
options passed into the JitsiMeetExternalAPI constructor, no logic
fires to actually change the audio output destination.

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.

* feat(welcome-page): be able to open settings dialog

- Create a getter for getting a settings tab's props so the device
  selection tab can get updated available devices.
- Be able to call a function from a tab after it has mounted. This is
  used for device selection to essentially call enumerateDevices on
  the welcome page so the device selectors are populated.
- Remove event UIEvents.AUDIO_OUTPUT_DEVICE_CHANGED. Instead directly call
  setAudioOutputDeviceId where possible.
- Fix initialization of the audioOutputDeviceId in settings by defaulting
  the audio output device to the one set in settings.

* squash: updateAvailableDevices -> getAvailableDevices, add comment for propsUpdateFunction

The Device Selection modal consists of:
- DeviceSelection, an overly smart component responsible for
  triggering stream creation and cleanup.
- DeviceSelector for selector elements.
- VideoInputPreview for displaying a video preview.
- AudioInputPreview for displaying a volume meter.
- AudioOutputPreview for a test sound output link.

Store changes include is primarily storing the list of
available devices in redux. Other app state has been left
alone for future refactoring.