This PR modifies the generateDc1InstCat.py script so that it will
1) replace stars with magnitude<min_mag with stars of mag=min_mag in the InstanceCatalog
2) keep track of the stars it replaced in catalogs named like output_dir/bright_stars_N.txt (where N is the obsHistID of the observation). These catalogs contain the uniqueId of the replaced stars and their true magnitudes.
This PR modifies the generateDc1InstCat.py script so that it will
1) replace stars with magnitude<min_mag with stars of mag=min_mag in the InstanceCatalog
2) keep track of the stars it replaced in catalogs named like output_dir/bright_stars_N.txt (where N is the obsHistID of the observation). These catalogs contain the uniqueId of the replaced stars and their true magnitudes.