Added novel_samples.py script and tests.

This new script outputs a TSV file with three columns:

- sample ID
- number of novel OTUs
- percent novel sequences

The output table is sorted by number of novel OTUs (descending). This table can easily be imported into a spreadsheet program such as Excel for additional sorting, filtering, etc..

Novel is defined to be an OTU that isn't found in the reference representative set (e.g. ```gg_97_otus_4feb2011.fasta```).

The script is accompanied by unit tests and script usage examples and test data.