Add preview window to configurator

[mrozycki]

For Christmas 2022 we were relying on an IP Camera app to do configuration, which allowed us to see what the camera is seeing on the phone screen. In June 2023 we were using a USB webcam and used Photo Booth app to line up the shot, but at that point we were doing only 2D setups, so the camera had to be lined up only once.

Right now we have switched to mainly using the iOS/macOS continuity camera capabilities, but with this setup there is no easy way to verify that the lights are all visible in the shot. The iPhone doesn't show what it's sending, and even if it did, OpenCV seems to crop the picture to make it horizontal anyway. Photo Booth cannot be used, since between capturing different perspectives, the configurator still has a lock on the camera.

The easiest solution would be to add a preview window to the configurator, which will show up when lining up the shot for next perspective.