Request full IIIF images by default in ElementImage

Closes #945 (closed)

This change forces all modals to always request the image at a width very close to the viewport's, which definitely will not make the bandwidth happy. It seems there has been a change that nobody really noticed, that was never requested or documented, during some refactorings in which the ratio was no longer used and I accidentally fixed it while working on the element preview dropdown. So a bug was actually a feature 🤔