DM-191: Measure and save aperture corrections in SFM

https://jira.lsstcorp.org/browse/DM-191
I've tended to avoid super unless I need it, because I find it harder to read and I there are some weird corner-case issues with it.  Don't have a strong preference, but I'd like to have a clear indication from above about which we should be using before worrying about changing it in any one place.