Added CRUDPersistenceService class

This adds a new persistence service class (CRUDPersistenceService). It extends QueryablePersistenceService so will work fine with all existing code that uses this class.

The class adds 3 new methods -:
update - to update a record in the store
delete - to delete a record in the store
getRecordCount - to retrieve the number of records for a particular item

The use case is to base the new mysql (and postgres) service on this class to allow additional features to be added via the REST interface to allow removal/modification of records if necessary (since rogue numbers do happen, and these can completely mess with a dataset)