Restore the behavior whereby small features are displayed in the
karyotype display using the diamond glyph, greatly improving their visibility,
and larger features are displayed using the generic glyph. This functionality
appears to have been inadvertently disabled by commit
68e13af301d5fcd76e884ecafcc88c30270e6444.

In the karyotype display, highlight features in a dark blue color to increase
contrast.
Merge pull request #46 from nathanweeks/issue/karyotype-feature-highlighting

Improve feature visibility in karyotype display