add dependent: :destroy relation to snapshots<->visualization
add dependent: :destroy relation to snapshots<->visualization

splashblot/dronedb,splashblot/dronedb,CartoDB/cartodb,splashblot/dronedb,CartoDB/cartodb,CartoDB/cartodb,CartoDB/cartodb,splashblot/dronedb,splashblot/dronedb,CartoDB/cartodb