Revert mapset download's background previews to the original size

[LavaLambz]

I'm unsure where to put this in but it's mainly about the mapset downloads so I am putting this here.

In mapset download pages, the background previews used to include more of the background until recently (after the new site) where it only takes a small center section of the background as the preview background. They look weird and less recognizable in my opinion. So I suggest you to revert them back to their original size, at least for maps submitted/updated after reverting this.