Simple Bounce option to prevent burn-in in displays

[NicoB1981]

I added a very simple extension that bounces the displayed text around a little bit in order to prevent burn in in displays.

I tried following the style of the project as close as possible but I do not work often in these type of projects (nor with github), so I appologise in advance, should my naïve additions overstep in any way.

Other than that, thanks for your work on the DesktopClock project and for sharing it - I intent to use it one one of my auxiliary monitors but I worry about burn-in in the display. Hence, my little contribution. But your work got me 95% there of what I need and want. Thanks.