merge qt_camera_error_handler into qt_camera_handler

[oltolm]

This PR merges qt_camera_error_handler into qt_camera_handler. When I tried to understand the camera code it seemed overly complicated to me, so I decided to simplify it.

[Megamouse]

The camera handler is not supposed to be a QObject. That's why

[Megamouse]

Just to explain: You're missing the Q_OBJECT macro that's needed for signals and slots. When I implemented this feature, it didn't work with the rest of the software (or didn't even compile. I don't remember exactly).

[oltolm]

Yes, I forgot Q_OBJECT. I added it and fixed the compilation error. Multiple Inheritance Requires QObject to Be First.

[oltolm]

I also merged qt_music_error_handler into qt_music_handler.