When left clicking and draging on webcam's output image (aka canvas) it should move the whole window.

When right clicking on webcam's canvas it should trigger the shooting just like left clicking on the red button.

These features also exist in audience (aka pantheon-videos)
right clicking on video canvas pauses or plays the movie
left clicking and draging on video canvas moves the whole window

So snap (aka pantheon-camera) and audience (aka pantheon-videos) became coherent.