OGM-444 Making NEO4J_GRAPHDB_FACTORYCLASS a private property
OGM-444 Fixing some stale JavaDoc links and a property name
OGM-425 Updating reference guide for OGM 4.1.0.Beta1

* Describing annotation-based and programmatic options
* Adding chapter for CouchDB
* Reflecting changes to property names
OGM-425 Incorporating review remarks
OGM-425 Update MongoDB native queries section in the documentation