Camera source buffer image capture

Add support for returning the captured image by the camera in a buffer somewhat similar to QVideoFrame. Both encoded formats (jpeg) and unencoded formats (DNG raw, YUV formats) should be allowed to be returned.
There have been already good discussion on the topic, and agreement about the needs during the Qt Multimedia Workshop. This was agreed it is a top priority issue for the 1.3 QtMultimediaKit.