On mobile Safari, when a user joins both audio and video muted, browser doesn't playout the remote audio because of a webkit bug. As a workaround, always add the audio track to peerconnection and then mute the track if needed.

* feat(prejoin) move invite to toolbar section

* feat(premeeting) redesign prejoin and lobby screens

* code review changes

* fix prejoin flicker and avatar id

* fix password error message and native lobby dialog close position

It is not 100% clear to me when it happens, but I think it could happen
in some race condition where a track is unmuted when it's being disposed
or something around those lines.

The fact is that any muted tracks are disposed by replaceLocalTrack(track.jitsiTrack, null) and they should not be used anymore.

Supposedly fixes a crash:

Failed to add local track to conference Track has been already disposed

Do not add the muted audio tracks to peerconnection until the user unmutes the first time. This applies to startSilent, startWithAudioMuted and startAudioMuted/startVideoMuted config.js settings.

When there's no jitsiTrack set on the base/tracks entry it means
a track is being created (get user media is in progress).

* 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.