Switch integ interface restore to Restorable
Switch integ interface restore to Restorable

after generalization in choderalab/openmmtools#140

dwhswenson/openpathsampling,openpathsampling/openpathsampling,jhprinz/openpathsampling,choderalab/openpathsampling,jhprinz/openpathsampling,dwhswenson/openpathsampling,openpathsampling/openpathsampling,openpathsampling/openpathsampling,dwhswenson/openpathsampling,openpathsampling/openpathsampling,choderalab/openpathsampling,jhprinz/openpathsampling,choderalab/openpathsampling,dwhswenson/openpathsampling