Stick to clean-css version 3.x.

Starting version 4.x clean-css is split into two packages and we should depend on clean-css-cli for versions 4 and above. Tested it and we have currently some problem with it like fonts and images got referenced under css folder. So sticking version to 3.x for now.

iTunes Connect/TestFlight requires these now and is not satisfied with
empty values anymore.

This reverts commit b96ca538e4. While iPad
support is nice to have, we are not ready for a publish in App Store.
During the upload to iTunes Connect, a verification of the .ipa fails
because:

- app icons for iPad are missing:
  - 76x76 pixels in .png format for iOS versions >= 7.0,
  - 167x167 pixels in .png format for iOS versions supporting iPad Pro,
  - 152x152 pixels in .png format for iOS versions >= 7.0,
- orientations required for iPad Mutitasking are missing:
  - UIInterfaceOrientationPortraitUpsideDown.

Now that Apple have approved build 1.1.185 for release in the App Store,
the short app version needs to be incremented; otherwise, no new builds
can be uploaded to TestFlight and, respectively, for release in the App
Store.

Simplify the source code (with the idea that source code which does not
exist does not have to be maintained).

Additionally, apply modifications to have the source code comply with the coding
style.

Overall, prepare saghul:audio-mode for merge into jitsi:master.

It's fired before creating the conference with lib-jitsi-meet.

* M1: device change now uses new flow.  fundamentally "works" but may be corner cases/side effects to other flows. haven't touched ffox yet

* M2: change toggle screenshare flows to use the new video replacement chain

* remove the old 'useVideoStream' and replace it with the new one

* use the new (and renamed back from the shim) 'dispose' method

* tweaks to work with the sdp overhaul changes in lib-jitsi-meet

* change the order in which we call dispose (to handle dispose being reverted back to how it is currently on master)

* move useAudioStream over to new flow

* restore useVideoStream doc

* handle rename JitsiConference::replaceStream -> JitsiConference::replaceTrack

* fix useAudioStream and useVideoStream to return a promise again

Iframe API - participant count

Recently, we reimplemented the Welcome page in React. Unfortunately, we
broke the checkbox that enables/disables the Welcome page and it would
allow checking but wouldn't allow unchecking.

Recently, we reimplemented the watermarks in React. Unfortunately, we
didn't take into account film strip-only mode.

Additionally, we duplicated watermark-related source code on the Welcome
and Conference pages.

Enable universal builds

A bug was discovered in d17cc9fa which would raise a failure to push
into the browser's history if a base href was defined. Fix the failure
by removing react-router. Anyway, the usage of react-router was
incorrect because the app must hit the server infrastructure when it
enters a room because the server will choose the very app version then.

React Native provides Platform.

feat(iframeAPI): implement avatar change commands