Allow passing an MDAnalysis AtomGroup as frames paramater

[PicoCentauri]

A direct passing of an MDAnalysis AtomGroup would be very helpful for people from the Bio molecular dynamics field.

As @Luthaf already mentioned one should implement a file similar to

https://github.com/lab-cosmo/chemiscope/blob/main/python/chemiscope/structures/_ase.py

A very useful additional parameter to be added, is an option to slice the frames to be shown. Since in MDAnalysis, the whole trajectory information is contained in a single object, it will require this additional parameter to allow users to select which frames they want to show. I think, this might be integrated globally for all supported frames object to maintain consistency

After a possible integration we can also promote chemiscope on the MDAnalysis website :-)