Facsimile loading too slow — needs indication that page has changed

[simongray]

When cycling through facsimile on glossematics.dk, e.g. https://glossematics.dk/app/reader/DJtilHJU-1932-06-23-tei-final.xml, oftentimes the facsimile loads too slow. Since there is no indication that a new facsimile is being loaded it makes sense to indicate this somehow... perhaps by removing the current image before loading the new one.