GStreamer: some improvements with the camerabin's capture settings.

GStreamer: some improvements with the camerabin's capture settings.

- Don't pretend we support changing the image or video capture
  settings while the camera is active. The pipeline needs to be
  restarted in order to renegotiate caps.
- Improved retrieving the supported capture resolutions and frame
  rates when using wrappercamerabinsrc. We now always get the
  supported values directly from the video source.

Change-Id: I107193288e370af105a25d16568a8f5a76022ada
Reviewed-by: Christian Stromme <christian.stromme@theqtcompany.com>