Structure.pbc_distance doesn't respect cell PBC settings

[Alexsp32]

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Currently, Structure.pbc_distance will check all periodic images of a periodic structure, even if it isn't supposed to be periodic in certain directions. (e.g. surface slabs with periodicity in x,y, but not z direction)

Expected behaviour: Use cell.pbc information to determine which periodic images to check for a closer periodic image in Structure.minimum_distance_translation.