Add histograms to gene scores page

[vsoch]

We want to add histograms to the /genes/XXX/scores/ and /genes/XXX/similar/ pages. I don't have time to work on this today so I'm opening the issue here for another day!

[vsoch]

A histogram was added to the gene similar page in #135, and this issue is re-scoped to add to the phenoyptic scores page. This will require a different strategy as this page uses server side rendering.