Perform lightcurve ELUT correction only at edges

[grazwegian]

Currently the lightcurve generator uses the same ELUT correction as spectroscopy where every science energy channel is individually corrected, given the broad energy bands usually used for the lightcurves it would make more sense for only the end edges of each band to be corrected the same way as is currently done for imaging.

[ennosigaeus]

This was discussed in today's weekly telco:

Ewan has some early-stage code, but it has not progressed much. Muriel has also started work on this, but only on the background detector. Since it is very similar to issue #194, it may be a good idea to assign this to Arun, too. Säm will talk to him.