New features: Document CRUD

+ Document:delete — Delete the current document using the current data.
+ Document::save — Updates or Creates and save the Document depending on Document::isNew.
+ Document::isNew — Document is new?
+ Document::create — Insert new record.
+ Document::update — Update assumed existing document.
+ Document::updateReferences — Updates references but does not save models to avoid infinite loops.
+ Document::getClientInstance — Return the Client reference.