Serializable datamodel pull

This pull request contains:

* Serializable implementation for the standard datamodel
* Extension to the ```DatamodelConverter``` that allow true deep cpoies (Draft)
* A ```TypeInspector``` class that simply can list the types involved in the structure of a given ```ItemDocument```. This was used for debugging purposes, but I found it a nice idea, so I included the draft
* A fix for the unknown JsonProperty in the ```JacksonPropertyDocument``` (again? I think it should already be in master)