Make line identification robust against wavelength shifts

Line identification needs to be robust against inaccuracies in the DetectorMap wavelength solution. While it's true the DetectorMap wavelength solution should be solid during observing, during development and commissioning and while dealing with both simulated data and LAM data, it's not unknown for the true wavelength solution to change relative to what's in the DetectorMap. Here's a possible algorithm:

• find and centroid all peaks in spectrum
• apply rough wavelength calibration to measured peaks
• for both observed and model line lists:
  • find pairs of lines with separations between 5A and 500A (separation is not too small to allow confusion, not too large to be very non-linear)
  • for each pair, calculate mean and difference
• match observed pairs to model pairs when the mean is within 50A and the difference is within ~ 0.5A
• Instead of pairs, could use triplets, and match the ratio of spacings.