cdodge/optimized-save-child-postition: create an optimized version of save_child_position which minimized the number of round trips to MongoDB
cdodge/optimized-save-child-postition: create an optimized version of save_child_position which minimized the number of round trips to MongoDB

don't refetch the current child, it's not really needed and it can be a bit expensive

edx-solutions/edx-platform,edx-solutions/edx-platform,edx-solutions/edx-platform,edx-solutions/edx-platform