Adding an ipython notebook to explore the benchmarks data

While the FACS metrics look okey, there's a significant issue with `fastq_screen`. The mean for `contam_fqscr` in `frame.describe()` shows `19`... it should never surpass 1, since it is a contamination rate!

Please have a look at my ipython notebook below for futher details on my data analysis (plots at the end).


http://nbviewer.ipython.org/github/brainstorm/facs/blob/d844a6ab/facs/utils/benchmarks_facs.ipynb


Next step: figure out why `fastq_screen` reports `56,05` as a contamination rate for `dm3` :-/

@arvestad, @guillermo-carrasco, @tzcoolman #reviewthis