The lobby feature adds the possibility to lock a meeting and only allow people in after virtually knocking and going through formal approval

* 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.

- re-add thepand icon, shaped like a pill
- round top corners