Optimized image sizes

Apart from maintenance work, today we released some optimizations for images. Before this update, images were not processed in the frontend, so when a 6000x4000 pixel image with 6.5 MB was uploaded, it was rendered like that in the frontend.

Those images were cached, so it was only somewhat slow on the first visit. Still, this could be improved.

Uploaded images are now much smaller by default and you can click on an image to see a bigger version of it, if available. This is enabled by default, nothing for admins to activate.

The same strong caching mechanism takes effect, so pages will load even faster now with a much more reduced network load time.