Dithering within an Observation unsupported

[Nat1405]

GN-2006B-Q-107 seems to dither within individual observations. The final cube merging isn't able to detect sub-observation dithering (yet).

This is a possible feature to add to nifsMerge if enough programs require it.

For now, a stop-gap check should be added in nifsSort.sortScienceAndTelluric() to detect this situation and handle it (either terminate the reduction or remove that directory from the list of directories to reduce).