PersistentDateTimeAsOneString: Chose some good descriptive variable names.
PersistentDateTimeAsUtcString: Rename from PersistentDateTimeAsOneString & StringColumnDateTimeMapper from DateTimeColumnStringMapper.
StringColumnDateTimeMapper: Externalise from PersistentDateTimeAsUtcString.
PersistentDateTimeAsUtcString: Add suppression for unused, damn reflection.