Fix Serialization for all fields of Document

[narad]

Updates to the wolfe data structures cause an error during unpickling when a Document doesn't have a dependencytree. I tried a few approaches to this - testing Option[DependencyTree] and DependencyTree - and nothing seems to work out-of-the-box even when using a special-purpose pickling object for SyntacticAnnotation. Some additional work needs to be done, but just to be functional on the Sentence/token level I've commented these out for now.