Add gallery page for planets, climates, etc (don't use plugin:gallery, but create a smoelenboek)

The idea is to have a page that displays the wealth of images we have on the wiki. This will help new users with forming an idea what kind of images to look for, and will also assist when someone is looking for an image, and is trying hard not to fetch one that is already used in some form (especially difficult with images of planets).

See Characters