Bug fix: Disease-gene associations

[joeflack4]

resolves #156

Changes

• Bug fix: Code for adding Disease2Gene relationships. These should be added if and only if there is one gene associated with the disease, unless it is a digenic disease/phenotype. However before, we were erroneously checking the number of diseases associated with a given gene.
• Delete: Code for adding Gene2Disease relationships
• Add; SPARQL query and goal to list relationships
• Added and updated comments related to gene disease associations

Resources

• Google Sheet of before/after results
• Tracker / discussion doc

[joeflack4]

@twhetzel This is no problem! It's on my schedule to do before Monday.