Add threshold tests to smoke output

[fitnr]

Please add a config option to set a minimum fire size and mass release thresholds before writing smoke outputs. Fires that are under these thresholds need not be written out in smoke CSVs. FYI @HoHsieh @mike-amodeo

[lautenberger]

Per our discussion last week, it seems that this test can be made exclusively on the basis of mass release and that we don't need to test for fire size. In the smoke-metadata branch I added the keyword PM2P5_RELEASE_MIN_FOR_OUTPUT to the &SMOKE namelist group. This is the threshold PM2.5 release - in micrograms - below which smoke files won't be dumped.

[lautenberger]

This is complete as of commit cfa2028dc5362c153c1256bab847d071664c458e.