Restart GUI when Video-Playback stalls

[MaZderMind]

In case of intermittent network issues, often one or more of the Video-Output stalls but the control-connection stays intact. The GUI does not restart in this case, because it only checks the control-connection. It should also restart, when one of the Video-Outputs stalls.

cc @danimo

[fightling]

or just display the loss and later reconnect automatically?

[MaZderMind]

While this has happened, it does not happen often. A single-digit-numer of times a year. Obviously restarting only the failed Video-Playback-Pipelines would be better, but as this is such a minor issue, a more rough solution restarting the complete Application would maybe also be ok.