Add reverse lookup and get_valid_residue in statements.py
Add reverse lookup and get_valid_residue in statements.py

johnbachman/indra,johnbachman/belpy,pvtodorov/indra,sorgerlab/belpy,johnbachman/belpy,sorgerlab/indra,jmuhlich/indra,bgyori/indra,sorgerlab/indra,sorgerlab/indra,sorgerlab/belpy,sorgerlab/belpy,bgyori/indra,jmuhlich/indra,johnbachman/indra,bgyori/indra,pvtodorov/indra,pvtodorov/indra,jmuhlich/indra,pvtodorov/indra,johnbachman/indra,johnbachman/belpy