Handle instruments that have dropped lines

Some instruments have dropped lines (i.e., lines that are not included in the PDS archive file, .img). ISIS handles this by adding the missing lines back into the ingested cub file as lines with NULL pixel values. ALE needs to correctly handle these.

MEX HRSC is an example. The information about which lines are missing is available in the line prefix data.

Chandrayaan1 M3 is another. The information is about missing lines is in the time table file.

Suggest looking at the ISIS ingestion applications to see which other instruments have this complication.

Example HRSC image with dropped lines: h1580_0008_sr3.img.
FYI this is a test image for the hrsc2isis ISIS application.