Do not show controls on home that are not clickable

[mprove]

The carrousel on the home https://iiif.io/ shows a set of screenshots or even animations. They contain control elements, that are without function in this context. e.g. the Zebrafish screen has a download and fullscreen control. They do not work as expected. People might get confused.

The usability issue is less severe on https://iiif.io/demos/ b/c the entire purpose of the page is to showcase many different cases.

I do not have a solution. Maybe downscale the screenshots. Maybe add a drop shadow to indicate a screenshot. Maybe embed the real thing.