Add mappers for qa-plot parquet tables

[timothydmorton]

The QA plots need (for now) to write parquet tables of the summarized source catalogs. This defines the filenames for those tables. I'm not sure whether it's OK to have qaTableVisit defined here with a blank template as I do, with then only template defined in obs_subaru, but maybe @PaulPrice can confirm?

[PaulPrice]

Check what other TextStorage entries do for python --- I'm not sure __builtin__.str works under py3.

[timothydmorton]

Good question...I see that FocusSweepPlot in obs_subaru uses builtins.str; is that better? I don't see any other TextStorage entries in obs_base.

[timj]

builtins.str is what you would use in Python3 or Python2+future. This has to work in Python3.

[jdswinbank]

__builtin__.str definitely fails on Py3. @sr525 figured out yesterday that builtins.str seems to be the right way to go.

[timothydmorton]

OK, I'll switch the others in obs_subaru to use builtins.str as well; this will save @sr525 having to dig that up in order to make pipe_analysis py3-compatible.

[jdswinbank]

lsst/obs_subaru@fda5411 :-)