Introduce navigation for all in-conference screens.

* 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

display sip address in invites
hide lobby password for sip users
tidy up invite placeholders

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