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.