Accuracy plots

Please have a look at the new accuracy plots:

http://nbviewer.ipython.org/github/brainstorm/facs/blob/269f1da73/facs/utils/benchmarks_facs.ipynb?create=1

As can be appreciated in the plots, both FACS and Fastq_screen are pretty much alike in terms of accuracy... FACS clearly beats Fastq_screen in performance, paying a price on storage though (to be done by @guillermo-carrasco on issue #105).

@henrikstranneheim, @arvestad, @luhugerth, #reviewthis