Separate animation module

[samwaseda]

Currently job.animate_structures only takes the positions from job["output/generic/positiosn"], but there are cases where we would like to have other positions, like if we measure running averages. So animate_structures should be a separate module.

[jan-janssen]

Some of this functionality is already included in https://github.com/pyiron/structuretoolkit/blob/main/structuretoolkit/visualize.py so maybe it makes sense to more the animation part to atomistics.