CIDEVSTC-201,202,203: Pyon enhancements for Postgres / REL2

This PR delivers these changes:

Refactored container datastore layer to support different datastore backends (CIDEVSTC-202)
Refactored couchdb datastore to comply with new datastore framework
Added PostgreSQL datastore backend (CIDEVSTC-201)
Provide Postgres search capabilities and geospatial column handling (CIDEVSTC-203)
Added couchbase datastore backend (experimental)
Added postgres and neo4j prototypes