Don't close call window right away
Reported by @guidog in https://source.puri.sm/Librem5/calls/-/issues/301
When one hangs up or the other side ends the call the call window is closed right away without any animation or status message so one sometimes thinks that the call just crashed. I think it would be better to keep the call window around for a second and display "Call ended" or something similar for a split second.
/cc @tobias.bernard
Related to #188