Checkin new version of DM-1466 on top of master.  Includes Russell's review.
DM-1466 changes for new C++ design, Flux algorithms
Changes for final code review of DM-1466
Merge branch 'u/pgee/DM-1466a'
Merge branch 'master' of git.lsstcorp.org:LSST/DMS/meas_base