Handle all levels of "sample" specification in get-all-orf-peptide-matches

[bmmalone]

Right now, the script is hard-coded to work with "cell-types" from the config file. It would be nice if it also handled samples (riboseq_samples" key) and conditions ("riboseq_biological_replicates" key).

• Add a command line option to the script to specify the level
• Add a function to ribo_utils.py which returns a list of the appropriate names
• Use this function rather than the call to ribo_utils.get_riboseq_cell_type_samples
• Add a function to ribo_utils.py which returns the appropriate "peptide__analysis" dictionary
• Use that in the loop

[bmmalone]

This will also entail finding the correct filename based on the level (e.g., "sample" filenames include lengths and offsets, while the others do not; the locations are different).

[eboileau]

See #88