Make EVCouplings Ellipses into Circles

[cannin]

@sacdallago Is it easily possible to change the EVCouplings div so that the markers look like circles? Why were ellipses chosen?

[sacdallago]

Overarching answer: no idea (why it was done how it was done nor how to make it into proper circles or anything else). I can just backtrack where the ellipses get generated: https://github.com/dfci/alignmentviewer/blob/master/CouplingsLogoDiagramD3.js#L67