Resolve "Error handling of non-periodic structures in ClusterSpace"

Summary of changes

• Add ValueError if atoms doesnt not have all pbc.
• Add unittest to test this.
• Added the same pbc check in get_primitive function since it won't work correctly if pbc are not True. (Also this will raise a ValueError if you try to create an FCM object with pbc=False)

@freeriks maybe you wanted to do the FCM pbc check another way?

Closes #210