Update code to find guide star candidates in guide camera footprints

Shuffle should select suitable guide stars in each of the six PFS guide cameras. 

The primary catalog will be GAIA and shuffle should automatically query GAIA (online) for each setup.

But also shuffle must allow for other catalogs (sdss, vizier) and manually supplied catalogs (e.g. from HSC pre-imaging).

Magnitude cutoffs, and minimum separation criteria should be freely configurable in the config file.