OAK-702: Optimize access to node type information

Merge EffectiveNodeTypeImpl and EffectiveNodeType (no need for an interface when there's just one implementation) to simplify refactoring

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1459750 13f79535-47bb-0310-9956-ffa450edef68