USB cameras that are 640x480 don't work

[RogerHardiman]

I have a USB camera that is 640x480 resolution. The gstreamer pipeline fails as it tries to open the camera at 1280x720

RPOS needs to check the width/height capabilities of the device first and then fall back to the right resolution.

Also if I change the Python code to set the width to 640x480, the ONVIF messages report 1280x720 so ONVIF Device Manager renders the video with the wrong aspect ratio.

So a few bugs. I'm sort on time right now to fix these so if any of the Python / USB cam contributors want to fix that, that would be great.