WIP: richer color priors

[jeff-regier]

This PR increases the number of mixture components for the color prior for 2 to 8. It also adds code that can dump a catalog of quasars in with the stars, for fitting the star prior. I didn't use it, however, for generating the included prior jld files, because it didn't seem to help. It's likely there are already a lot of quasars mixed in with the stars that the star prior is fit to.

Color is looking pretty good now for the FFT version of Celeste. missed_stars improves but missed_gals gets worse. Results for the MOG version of Celeste are more-or-less unchanged.

FFT Celeste:

│ Row │ field        │ primary   │ celeste   │ diff        │ diff_sd    │ N   │
├─────┼──────────────┼───────────┼───────────┼─────────────┼────────────┼─────┤
│ 1   │ position     │ 0.243098  │ 0.264657  │ -0.021559   │ 0.00913341 │ 417 │
│ 2   │ missed_stars │ 0.0263789 │ 0.0551559 │ -0.028777   │ 0.00996414 │ 417 │
│ 3   │ missed_gals  │ 0.0455635 │ 0.0479616 │ -0.00239808 │ 0.010722   │ 417 │
│ 4   │ mag_r        │ 0.189753  │ 0.286899  │ -0.0971467  │ 0.0232656  │ 416 │
│ 5   │ color_ug     │ 1.25994   │ 0.760379  │ 0.499559    │ 0.0588663  │ 370 │
│ 6   │ color_gr     │ 0.30301   │ 0.221951  │ 0.0810593   │ 0.021301   │ 413 │
│ 7   │ color_ri     │ 0.18629   │ 0.149705  │ 0.0365845   │ 0.0152487  │ 416 │
│ 8   │ color_iz     │ 0.285698  │ 0.188256  │ 0.0974421   │ 0.0245772  │ 417 │
│ 9   │ gal_fracdev  │ 0.260406  │ 0.222467  │ 0.0379387   │ 0.0235699  │ 173 │
│ 10  │ gal_ab       │ 0.189946  │ 0.144821  │ 0.0451247   │ 0.0118508  │ 173 │
│ 11  │ gal_scale    │ 1.54675   │ 0.635045  │ 0.911707    │ 0.849901   │ 173 │
│ 12  │ gal_angle    │ 17.6112   │ 12.7528   │ 4.85847     │ 1.74086    │ 81  │

MOG Celeste:

│ Row │ field        │ primary   │ celeste   │ diff        │ diff_sd    │ N   │
├─────┼──────────────┼───────────┼───────────┼─────────────┼────────────┼─────┤
│ 1   │ position     │ 0.243507  │ 0.235864  │ 0.00764326  │ 0.00718287 │ 416 │
│ 2   │ missed_stars │ 0.0264423 │ 0.100962  │ -0.0745192  │ 0.0136263  │ 416 │
│ 3   │ missed_gals  │ 0.0456731 │ 0.0288462 │ 0.0168269   │ 0.00971837 │ 416 │
│ 4   │ mag_r        │ 0.190117  │ 0.193283  │ -0.00316549 │ 0.0151386  │ 415 │
│ 5   │ color_ug     │ 1.26319   │ 0.739217  │ 0.523971    │ 0.05909    │ 369 │
│ 6   │ color_gr     │ 0.303688  │ 0.183274  │ 0.120414    │ 0.0158518  │ 412 │
│ 7   │ color_ri     │ 0.186722  │ 0.121602  │ 0.06512     │ 0.0152953  │ 415 │
│ 8   │ color_iz     │ 0.286331  │ 0.148811  │ 0.137521    │ 0.0213394  │ 416 │
│ 9   │ gal_fracdev  │ 0.260406  │ 0.201785  │ 0.0586206   │ 0.0222382  │ 173 │
│ 10  │ gal_ab       │ 0.189946  │ 0.139962  │ 0.0499837   │ 0.01129    │ 173 │
│ 11  │ gal_scale    │ 1.54675   │ 0.58806   │ 0.958692    │ 0.850291   │ 173 │
│ 12  │ gal_angle    │ 17.6112   │ 12.8144   │ 4.79685     │ 1.752      │ 81  │

This PR closes #14 and closes #16 once no it's no longer a work in progress.