[Fixed 80301910] Fixed failures saving and copying documents:

1. Saving documents that contained no postmessage enabld DI were failing.
   Found this was due to callback not bound to proper context.
2. Copying documents failed after merge of Post Message and Autosave pull
   requests. This was due to copy logic being written for synchronous
   save logic, while the postmessage change makes creating a document to
   save into an asynchronous process. Rewrote the body of copyDocument to
   be a callback.
[Fixed 80161868] Connect documents to their proper contexts when opening.

See bug description. Changes made by Bill.