Replace obsid obsnum calculation with HERA standard.
Replace obsid obsnum calculation with HERA standard.

add_obs_librarian now looks for obsid in file header,
nominally placed there by the correlator.

If it doesn't find uv['obsid'], it converts the jd
in the filename into a gps time and uses the floor
of that.

HERA-Team/librarian,HERA-Team/librarian,HERA-Team/librarian