Propagate flag information from arc/sky line files into e.g. reduceArc

There are two sets of flags used for reference lines, and they conflict. Please add the ones used in e.g. skyLines.txt or ArCdHgKrNeXe.txt to the ones defined in ReferenceLine::Status (n.b. this will require changing the values in the .txt files).

Then fix readLineListFile to use these values (which looks as if it's just a comment).

Once this is done, we need to fix reduceArcTask to read all the lines, above an intensity threshold, and match all of them before discarding the ones labelled as being e.g. blends.

This is necessary as some of the OH lines are blended, so they are marked as such (currently 2) in the skyLines.txt file. However, reduceArc drops lines with status != 0, so when it goes to match lines it doesn't know that there is a line, but it shouldn't use it, and instead makes a bad match.

There are some lines labelled 1 for not-visible. We'd either need to exclude them from the line matching, or reset their intensities to 0, or better mask them out on read (using the flagsToIgnoreMask argument to readLineListFile); I think it'd be better not to read them at all, as otherwise they'll confuse the debug plots.