Power

The power analysis notebook. Expanded notebook text is on [google docs](https://docs.google.com/document/d/1CQPlAue1mVFOd811cKGuy4fibFs5abR-wTjaeW6Wu0I/edit?usp=sharing).
See this: https://github.com/biocore/qiita/pull/643, it's the fix implemented in qiita.