Examine: Improve Karyogram interactivity & info

Karyogram now has 1) clickable chromosome labels 2) expands to fit the
full width of the page 3) doesn't overflow its bounding box 4) is
colored by the number of variants in a given bin.
Examine: Karyogram improvements (Address CR)

Style css, center chromosome labels, rename things, tidy.
Examine: Karyogram changes

Update pdiff tests, fix VCFTable test rename.
Update pdiff screenshots
Merge pull request #158 from hammerlab/issue-65-color-karyogram-by-variant-freq

Examine: Improve Karyogram interactivity & info