Fix for GPMONGODB-281 "Memory leak when instantiating large amounts of objects"

New stateless session mode that allows users to map an entity as stateless and have its state not kept the session. This allows mapping domain classes to much larger MongoDB datasets
Improvements to stateless mode for  GPMONGODB-281 "Memory leak when instantiating large amounts of objects"
Fix failing Neo4j tests, by allowing disabling of auto timestamping
Merge branch '1.x'

Conflicts:
	grails-datastore-gorm-mongo/src/test/groovy/org/grails/datastore/gorm/mongo/MongoSuite.groovy
	grails-datastore-gorm/src/main/groovy/org/grails/datastore/gorm/GormInstanceApi.groovy