add method to retrieve uniprot IDs from a PDB ID

Former-commit-id: ab2cfde9fd3ad61a96722b9ef81bae42f2213f54

ippisite/ippidb/ws.py

@@ -78,3 +78,8 @@ def get_pfam_info(pfam_acc):
     domain_family = ''
     return {'id': pfam_id,
             'description': description}
+
+def get_pdb_uniprot_mapping(pdb_id):
+    resp = requests.get('https://www.ebi.ac.uk/pdbe/api/mappings/uniprot/{}'.format(pdb_id))
+    uniprot_ids = list(resp.json()[pdb_id]['UniProt'].keys())
+    return uniprot_ids