Handle wavelengths out of order

[Jason Wang]

IFS images taken at the same time but at different exposures could come with wavelengths out of order. This is ok, except the output IFS data get saved with the wavelengths in the header in increasing order. We need to always order the wavelengths at input, or handle misordered wavelengths when recording the output. The data is fine – it’s just the documentation in the output that needs to be fixed.