Fixes: https://github.com/jitsi/jitsi-meet-electron/issues/124

Wait until the joined event.

Also, create a couple of auxiliary functions so we save some indentation
in the main render function.

Fixes: https://github.com/jitsi/jitsi-meet-electron/issues/103



Co-authored-by: Akshit Kr Nagpal <akshitkrnagpal@gmail.com>