added split_aggregate_ref and aggregate_ref methods; added sort key to dimension level (not yet used); changed level repr to be a dict repr;
added split_aggregate_ref and aggregate_ref methods; added sort key to dimension level (not yet used); changed level repr to be a dict repr;

cesarmarinhorj/cubes,cesarmarinhorj/cubes,pombredanne/cubes,ubreddy/cubes,zejn/cubes,jell0720/cubes,ubreddy/cubes,zejn/cubes,zejn/cubes,noyeitan/cubes,she11c0de/cubes,cesarmarinhorj/cubes,pombredanne/cubes,pombredanne/cubes,jell0720/cubes,she11c0de/cubes,ubreddy/cubes,noyeitan/cubes,noyeitan/cubes,jell0720/cubes,she11c0de/cubes