New acceptor molecule workflow needs a tweak to the indexing

[JimmyRushing]

An adaptation of this workflow

https://github.com/cmelab/morphct/blob/master/examples/new-acceptor-molecule-workflow.ipynb

worked for @chemicalfiend (@gwenwhite) on y6 and, because y6 and BTO have the same number of atoms, it should work for any mixture of these two. However, with some clever numpying, the code that automates the chomophore list building could be modified to handle any mixtures.

[chemicalfiend]

For reference : the tweaking that I made involved adding my own dictionary with the missing atom types from amber_dict . I'll try making a workflow for acceptor mixtures and push it to examples.