REL-1535: Display effective NIFS OIWFS FOV corrected for offsets.

Trying to reintegrate a change from September 2012 that was somehow lost in space and time at some point. Seems simple enough but I am a bit lost at the point where originally an array of OffsetPosLists was taken from the program. I assume this has to be replaced with information taken from _iw.getContext().offsets() but I am not sure which one to use in this context. Before spending more time  digging through old/new code I hoped maybe @swalker2m could shed some light on this; see TODO comments in code.
Right, I think you can get the "science" (i.e., guided offsets) positions directly from `Set<Offset> offsets = _iw.getContext().offsets().scienceOffsetsJava()`.