DragDrop fix for multiple connected sortables

Checking if ui.sender is set by sortable(). If it is, the dragged item is coming from another sortable list.
ngMove() added - responsible to move the object from the old sortable's array to the new one.
ngUpdate() removed (as no apparent functionality)

Minor modifications - unique droppable id is used for sortable identification and as key for item arrays within $scope.items object.