Include IDs in Star (centroid) objects

[markasoftware]

Keeping track of centroid indices is a PITA in star-id algorithms right now. For example, if you have a function that needs to operate on a subset of the centroids, it is currently necessary to pass the full list of centroids, and then another list of centroid indices that you want to work on, instead of just passing a list of centroids (or pointers to centroids), which would be cleaner.

(Similarly, it might be good to include indices in CatalogStars after narrowing. Yes, we have names right now, but those names don't allow fast lookup into the full Catalog).