Made OTU category significance code more robust.

Sometimes FDR-corrected p-values are listed as 'NA' in the results file, and this was causing the script to crash. If the FDR-corrected p-value cannot be converted to a float, the Bonferroni-corrected p-value is now used instead.
Data files are removed on a per-individual basis.

Fixes #106.
Relaxed generate_participant_list.py file format.

Fixes #105.
Merge pull request #107 from jrrideout/robust

Misc. fixes/changes