Deprecate SerializableDataSet

Because DataSet has several elements that need to be typed, there is no default way to just serialize it. Instead, you need to stuff it into a SerializableDataSet first. The point of this is to specify lists of field and cell types that might be encountered. This, however, is of dubious value anymore. Instead, there should be a precompiled function that serializes a DataSet for default types, and SerializableDataSet should be deprecated.