Set the current document title to the first title in pasted text
Set the current document title to the first title in pasted text

1. Register a listener to Ace's paste event
2. Check that the document is still untitled
3. If so, register a one-time listener on `preview.updated` to detect when the Markdown is parsed
4. Find the first header in the Markdown (if there is one) and set the Document's title to it

I had to pull in the documentsService to the user controller to read and write the document's title

joemccann/dillinger,joemccann/dillinger,joemccann/dillinger