Cadnano 2.5 appearance has always been a bit off. I realized one reason why is that the endpoint QPen should be set as cosmetic, so the outlines get drawn with a thicker stroke when zoomed out.
I made other tweaks and changes such as line widths, default colors, etc.
Another issue is the exit points of the crossover lines. They just look better centered.
This is also an example of a legacy import bug.
Fwd and Rev filters don't make sense anymore, we need oligo-level locking.
Ported http://stackoverflow.com/questions/35129052/ to PyQt5.