Final batch of improvements to plot-ll-map.py

1. Use list of nicknames so that we pick up the LV knots, etc
2. Skip the sources listed in problem-sources.txt
3. Get data for close-in sources from `Jorge_prop/PC-will` folder
4. In case that A' < 1.5, use the average PA of the actual arc points
   rather than the PA deduced from the circle fit, since the latter is
   not very accurate for small A'.  The source ID text label is colored
   to reflect whether this is done or not.
5. Cunning octant-based alignment of the text labels
6. Sources listed in `interproplyd-sources.txt` have their label box
   colored orange
7. Read in the list of objects from
   `luis-programas/arcs-summary-merge.tab` instead of from
   `ll-data.json`