Bokeh pca

Proof of concept of performing PCA with bokeh. Tooltips on each sample show every column of the metadata, for that sample.

![image](https://cloud.githubusercontent.com/assets/806256/5437968/58c64d64-8429-11e4-9386-769eba50a136.png)

Future steps: https://github.com/YeoLab/flotilla/issues/204