Experimental VA drug class relationship walking

With 5 rounds this covers 74.5% of all RXCUIs with these TTYs: 'SCD', 'SCDC', 'SBDG', 'SBD', 'SBDC', 'BN', 'SBDF', 'SCDG', 'SCDF', 'IN', 'MIN', 'PIN', 'BPCK', 'GPCK'
Enable Couchbase
Improvements
Add NDC lookup method
Switch to Mongo

Leave Couchbase code in place; switch is motivated by availability of MongoHQ.