Add argument to automatically apply mask to QC'd data

[blaylockbk]

Currently, if you apply additional Quality Controls on the data (``) that data is stored in the DataFrame attributes. The README file describes how you can mask the flagged data, but it would be nice if this were done automatically, as a Boolean argument when the DataFrame is created.

(See https://github.com/blaylockbk/SynopticPy#-how-to-set-synoptics-quality-control-checks)