#377 AE, allow option to add exons with low scores

[Brian O.]

AE41) Sima wrote:
Now I see a repeatable bug with clicking and dragging an exon on Linux,
with the gene CG4432. If I pull down the sixth genscan exon, which is not
a part of the annotation yet, and try to add it to a transcript of CG4432,
apollo won't let me add it, it only allows me to make it a new non-overlapping gene. I am dragging and holding down the shift key, and it
works with other genscan exons.

[This is due to that exon having a very negative score that's out of the range for genscan listed in game.tiers. There's another genscan
(lavender) exon with a negative score that won't drag properly either. If I change their scores to be positive, they drag fine.]

[Temporary fix: enlarged genscan range in game.tiers. Mark suggests a
more general fix:
DraggableFeatureView can somehow tell its CFTM not to bother testing
for score. The fact that the user could drag the thing means that the feature was being displayed and therefore it somehow managed to pass a
threshold test. Therefore theres no need to subject it to another threshold test. This may be the way to go.]