Split fitsviewer tests into several modules.
Fixed bug in CutoutGrid where all frames were sharing the same list.
Triplet focus calculator now centers on the source in the specified frame,
not the source in the current reading.
Fixed vertical ordering of triplet frames.
zscale images in triplet individually.
Merge pull request #199 from drusk/triplet_frames

Triplet frames
Merge remote-tracking branch 'origin/master' into track