Update OrderbookYaml and DotrainYaml to output yaml string

[findolor]

Currently we don't have a way to output a full yaml string in both of the yaml data structures. This prevents us using the internal data for these structures in hashing for example. During the state serialization logic in gui, we only hash the dotrain content which is incorrect because we merge additional content using separate yaml strings. It is a bug if we only used dotrain content as other data is also used.

We need a function to go from an OrderbookYaml/DotrainYaml to a yaml string