Also allow downloading the preview image instead of the original

[japsu]

Originals can be huge (like, 20 MB huge). For many use cases the preview image would be more than sufficient.

Change the "Download Original" button to a dropdown that lets you choose the format to download.

Example:

Web page: https://conikuvat.fi/desucon-frostbite-2020/yleiskuvat/jenni-suominen/img-6106
Original: https://conikuvat.fi/media/pictures/desucon-frostbite-2020/yleiskuvat/jenni-suominen/img-6106.jpeg (4 MB)
Preview: https://conikuvat.fi/media/previews/desucon-frostbite-2020/yleiskuvat/jenni-suominen/img-6106.preview.jpeg (350 KB)