#123 Finished getting literature for diseases

Implemented:
1. New literature list containing objects with type, obj, and pub. Each pub is a PMID ID.
2. Literature list is composed of resources from gene_associations, phenotype_associations, and alleles.

To Do:
1. Represent literature as sortable table.
2. Use LiteratureService to get author/date/citation from each PMID.
#123 Created table for literature tab in disease pages

Implemented:
1. Literature is represented in sortable table.

To Do:
1. Use LiteratureService to get author/date/citation from each PMID.
2. Add literature tabs to phenotype, gene, and model pages.
#123 Added checks to avoid crashing on TypeErrors
#123 Added literature tab to phenotype pages
#123 Finished adding literature tabs to gene and genotype pages

Implemented:
1. Finished literature tabs on all disease/phenotype/gene/genotype specific pages.

To Do:
1. Use LiteratureService to get author/date/citation from each PMID.
#123 Fetching from literature call

Implemented:
1. Fetching XML from literature services call. (I couldn't find/didn't know how to get results in .json.)

To Do:
1. Parse XML to JSON for displaying on pages.
2. Parse JSON object fetched from NIF literature services call into author/journal/year for display as separate columns of table.
#123 Disease page literature tabs work fully!!!
#123 Literature tabs completed for phenotype pages
#123 Fixed bug in disease page literature tabs

I was not correctly fetching PMIDs from the disease_association object. Works correctly now.
#123 Finished literature tabs for gene and genotype pages
Merge remote-tracking branch 'upstream/master' into literature-tab
Merge pull request #365 from monarch-initiative/literature-tab

Literature tab