DATAMONGO-479 - Add support for calling functions. 

We added `ScriptOperations` to `MongoTemplate`. Those allow storage and execution of javascript function directly on the MongoDB server instance. Having `ScriptOperations` in place builds the foundation for annotation driver support in repository layer.
Good point. Yes, would have been for calling scripts via `ObjectId`, but once I tried to do so it turned out that one can store the script using `ObjectId` but won't be able to call it later as the name needs to be a `String`. Should be `String` instead of `Serializable` then.