Implement Sifts-uniprot-isoform specific alignments and protein chain's 'best uniprot ID'

[ChrisMoth]

Sifts has introduced a RESTAPI that aligns PDB chains to isoform specific uniprot IDs. Create plumbing code to populate our database with the new sifts_mappings_pdb_uniprot_all_isoforms table, as well as retain the sifts_legacy_xml which provides robust non-isoform specific alignments