Add a loading indicator to the Examine page

Here's a screenshot of the page while it's loading:

![loading](https://cloud.githubusercontent.com/assets/98301/4325069/05872cde-3f61-11e4-95a1-507958356571.png)

I believe the Karyogram doesn't show up because it hasn't loaded the cytoband.tsv file yet.

Fixes #38.