#1067 Add user preference for different default camera

[Matija Nalis]

When using Camera2 API, user can cycle through different cameras. However, those cameras always start 0 when OpenCamera is started, which is annoying for example if user almost always uses wide-angle camera 3.

That can be solved by changing hardcoded cameraId_default in code and recompiling (and that only after applying fix in MR 67!), but it would be way more accessible and user friendly if users could choose default camera in preferences.

Would it be possible to add such "Default camera ID" preference?

[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)