bisqremote: Screen flickers

I seem to be using the webcam wrongly. The java app makes my screen flicker sometimes at startup or shutdown. Maybe this is due to using the wrong thread.

Start by reproducing the screen flicker during application startup and shutdown, then trace the webcam-related code and thread usage. The issue provides no file, test, or entry point; done means identifying and fixing the cause so the screen no longer flickers in either lifecycle phase.

Written by the indexing model from the issue text.