Fix several missing images and videos that didn't get imported correctly.

This handles the first part of #13 (closed) by fixing some broken images.

There's one artists interview I'm unsure of: that one had apparantly been hotlinking to the artist's origin website. I could find the image on archive.org, should I copy it in?

Also, the 5.1 release notes need to be tested: I'm unsure if it's linking appropriately to the video files.