Per-city chip catalogs

[pkerins]

Having a master chip catalog has been convenient, but at this point it has become impractically large and cumbersome. As a result, following work on incorporating multiprocessing into chip creation, we are officially moving to per-city catalogs, ie one catalog per city containing all chips for that city. The naming convention will be chip_catalog_city.csv; catalogs will be housed in a dedicated folder in the data_root directory; currently this would be /data/phase_iv/catalogs/.

The code base requires a small amount of additional infrastructure to handle these separate catalogs. Additionally, the original master catalog needs to be disaggregated into appropriate per-city catalogs, named properly and saved to file in the appropriate locations.

[pkerins]

To clarify, in addition to the creation of the files themselves, I want some accessor functionality in the code base so that the user can simply pass a list of cities and get back a catalog with all chips from said cities. (Tempting to have this perform filtering as well, eg return only specified images from specified cities, but ultimately the catalog files have to be loaded anyway, so might as well keep things modular.)