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.

fixes #29 fixes #65 fixes #114 

![](http://cl.ly/image/1Y043B3d2103/Screen%20Shot%202014-10-27%20at%205.33.30%20PM.png)

(NB: still can zoom out infinitely; want to improve binning, make it more dynamic; doesn't resize when the window is)
Some kind of high level description would be helpful. Points to hit would include things that are specific to this use of Idiogrammatik, e.g.:

- Colors the karyogram according to variant density
- Ignore scroll wheel unless "focused" (and what focused means)
- Shows density of all records; does not update according to filters.