Allow to display document content in case of Create document notification

In the case of receiving a notification about a Create event (should be true for an Update event too, when we'll support it), we should allow to display the content of the created document, without having to go to the actual location of the document.

Since it all depends of what's sent on the message, in case of XWiki document creation / update, we should send the HTML content of the document as part of the message.