Filtering notebook

The filtering notebook for removing bloom sequences. Rendered version of the notebook is [here](http://nbviewer.ipython.org/github/wasade/American-Gut/blob/e9f79334c41da6f5184e9372473eca076398507d/ipynb/FilterAndPickOTUs.ipynb) and the updated index is [here](http://nbviewer.ipython.org/github/wasade/American-Gut/blob/e9f79334c41da6f5184e9372473eca076398507d/ipynb/index.ipynb).