When Firefox users choose a new device via the gUM prompt store
these as the new user selected devices, so they show up in the
settings menu.

* fix(conference) avoid double prompts in Firefox after choosing non-default device

* addressed linting errors

- 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

* 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.

* ref(device-selection): do not override var that is not reference again

* ref(device-selection): do not override var that is not reference again

* ref(device-selection): always update known devices on device list update

* ref(device-selection): replace call to get devices from legacy to redux

* ref(device-selection): remove unused device list state from mediaDeviceHelper

* ref(device-selection): update store before updating UI

Prepares for the latest eslint & flow-related npm packages which cause
these errors.

ESLint 4.8.0 discovers a lot of error related to formatting. While I
tried to fix as many of them as possible, a portion of them actually go
against our coding style. In such a case, I've disabled the indent rule
which effectively leaves it as it was before ESLint 4.8.0.

Additionally, remove jshint because it's becoming a nuisance with its
lack of understanding of ES2015+.

- Create a notification component for displaying a toggle.
- Create an action for showing the component if allowed by
  the local storage setting and for saving the setting to
  local storage.
- Remove all notifications having a timeout by default so the
  device error notification must be dismissed manually.
- Split the camera and mic error dialog into two separate
  notifications.

Make toolbar's microphone button enabled whenever there are any
'audioinput' devices available and allow to add audio during
the conference even if microphone permissions were denied on startup.

Dynamically enables/disables the toolbar video button. Prior to that
commit if we would start with no video there would be no way to enable
it later on.

Enable ESLint on jitsi-meet with the same configuration and the same
goals as in lib-jitsi-meet.