Genome visualization

This creates a genome browser to visualize aligned reads in a reference region, which can be changed by moving left/right, zooming or typing the specific region. Hovering over a rectangle shows the name of the read. The height of the SVG container with the rectangular reads changes based on the number of tracks. (The variables passed into freq.spp and reads.ssp are counterintuitively being parsed from String to Int because they kept getting formatted with commas, even when I tried to replace them...) !

Here is the visualization at /freq for the frequency of reads at a region: 
![freq](https://cloud.githubusercontent.com/assets/4754931/3836188/9aeb8522-1dce-11e4-92a1-21f2ac3a722e.png)

Here is the visualization at /reads for the overlapping reads: ![screenshot](https://cloud.githubusercontent.com/assets/4754931/3831402/0faf3264-1d93-11e4-8cca-5c699e0e7c74.png) This is built off of @tdanford's visualization work. Thanks!

Please tell me if you have any suggestions; I only have 3 more days left in this internship and I'd love to get this merged in.