Make scenery group icons centered like they are in the built-in inventions list

[KatieZeldaKat]

The icon is not centered in the invention manager:

The built-in inventions list for reference:

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It's also possible that scenery themes will get their own custom images as well. If this ends up being the case, then these new images will end up fitting perfectly. As such, we wouldn't need to worry about offsetting the images to match the built-in inventions list.