v4l2 update function, video source size change, "check" unit test system integration

This part of the project on dynamic change the resolution depending on the quality of the communication channel. v4l can change resolution of the cam, so, i think this is a useful feature.
adding a static pointer to the "current" video-source state means that you can have only 1
video-source in the application, this is a limitation which I think that we dont need.
the video-source framework should be re-entrant enough, so that the application can open
multiple devices, either with the same name or different devices.