Add alphafold fetch for mutation scores sequences

[Tom Goddard]

Add a button to the Mutation Scores panel to fetch an AlphaFold database predicted atomic structure for the sequence of opened mutation data. The main purpose of the ChimeraX mutation capabilities is to color structures using mutation data. While an experimental structure is often available it helps to include all the disordered loops and N and C terminal portions because mutational scans include those functionally signficant residues. Using an AlphaFold prediction serves this purpose.

Their may not be an exact sequence match from the AlphaFold database. In that case open the closest sequence and associate the structure with the mutation data using a sequence alignment.

[Tom Goddard]

Done.

If the mutation set is fetched from MaveDB it usually has a UniProt identifier. In that case the AFDB model for that UniProt identifier is fetched. Otherwise a sequence search based on the implied sequence of the mutation data is done using the "alphafold match" command which does a k-mer search to find the best matching AFDB model.

Added documentation for mutation score alphafold fetch.