Galaxy image tweaks

**Bumps savegame** 

Re-spin of #3195, as it turned out that's easier to let the images match coordinates than the other way around. Had to rotate the density map, that's why the savegame bump was necessary.

@Baobobafet / @fluffyfreak 
Before merging, I would like to know the source and license of the image, so I can add the information.