Added a superimposed padlock to the blurred screen

I added a superimposed padlock to make the screen less ambiguous and give your eyes something to focus on when you look at it (this was causing me a lot of eye strain). Maybe this would be best as a command-line toggleable option?
877/1280 is the actual width/height ratio of the lock image, as imagemagick as issues detecting this from the SVG file.

Scale is used on line 107, so that the lock is not 100% of the screen height.