add an Ar line to the tracked list of short arc lines

[sybenzvi]

Now that #414 is closed, I realized the calibration DB is not tracking any lines from the Ar lamp. If we have to add one, a reasonable choice is the relatively well-isolated λ9125 line (typical integrated flux is <1k). Once it's added, we have to:

• Rerun QA for all short arc exposures.
• Refill the calibration database to update the affected exposures.
• Recompute reference levels for this line.
• Add any related plots to the per-exposure and historyqa pages.