adding the sv1-summary.py script in bin

[araichoor]

This PR adds the sv1-summary.py script in bin/.
The principle of this script is to have a single script producing overall information about the observed sv1 tiles.
It produces:

• sv1-exposures.fits: this is a per-exposure file with hopefully all the useful columns; I "ingest" gfa information from Aaron, and produces {brz}_depth estimate using routines from David Kirkby;
• sv1-tiles.fits: a simple file with the coordinates of the tiles, to feed desitarget.io routines;
• sv1-skymap.png: sky map of the tiles;
• sv1-depth-{qsolrg,elg,bgsmws}.png: a display of the r_depth per exposure;
• sv1-tables.wiki: a text file with tables to be copied-pasted in the wiki (1)tile design, 2) nb of targets, 3) nb of observed exposures per tile, 4) gfa+depth estimations per exposure, grouped per tile).

The idea is to run this script ~daily, and then update the wiki page https://desi.lbl.gov/trac/wiki/SurveyValidation/SV1 accordingly.

The depth estimation routines are courtesy of David Kirkby.