Matija Nalis

(Implementing it might also help users for whom cycling cameras doesn't work correctly, see e.g. https://sourceforge.net/p/opencamera/tickets/1058/#5e18)

(of course it would be best if cameraId would be selectable in preferences as requested in #1067 and/or saved between restarts; but implementing that would still need this or similar fix)

Add user preference for different default camera

I've submitted MR 67 to implement it.

fix cameraId_default so changing it actually works

(of course it would be best if cameraId would be selectable in preferences and saved between restarts; but implementing that would still need this or similar fix)

make cameraId_default work