Update the DPDD to clean up the discussion of maggies vs. Janskys

From the September 12, 2017 PST Meeting:

3) How will LSST report flux measurements?

Short discussion ended without much controversy. Robert, as Calibration Scientist, didn’t raise any objections. Chris expressed unhappiness that we’d call our flux units Jansky, instead perhaps "pseudo-Jansky” (Jansky is a unit for the specific flux, not a broad-band measure). Since no other survey ever had a delta function as their bandpass, every other survey that reported flux in Jansky is guilty, too. If you find this discussion exciting (Robert said he didn’t), please read https://github.com/lsst-pst/fluxunits/blob/master/fluxunits.pdf

Action item: Mario will propose a revised text for DPDD (switch discussion weights
given to Jansky and maggies).