Add support for Document Composition

Having a simple merge of fields is interesting, but for some use cases we need to go further.

Typically, if the Document I want to render is a Note I would like to keep the formating of the Note contents inside the rendered Document.

In such a case we have :

• the template that manages
  • cover page with logo
  • history of the document
  • index
• the Nuxeo Note Document that provides
  • Fields data (Title, author, creation date, history info ...)
  • Blobs (pictures)
  • the formatted text content

XDocReport provides some experimental support for text styling that allow to integrate HTML and Wiki markup inside ODT and DocX files.
We will probably need to extend this, but since the system is pluggable this should not be a real issue and anyway it's far more simple that really merging 2 documents with their style (tested this in the prototype )