[mbeddr.doc] Add support for documentation that includes mbeddr.doc paragraphs/images

[HeikoBecker]

Currently, a user of mbeddr.doc cannot use images or other mbeddr.doc elements to write documentation in-place with this infrastructure.

The IDocumentable interface allows to attach a single paragraph documentation via the addDocumentation intention (node url, node attributee)

Ideally, mbeddr.doc provides a new interface, e.g., IHaveRichDocumentation, that supports documentation similar to the documentation written in mbeddr.doc sections (i.e. multiple paragraphs to support images and the likes).

The new interface should be interoperable with the old interface. If the intions and documentation of one is shown, the documentation and intentions of the other should not be available. For existing cases, an error/warning should be raised.

This functionality should also be integrated with the documentation viewer from the mbeddr.doc aspect which currently checks only for the documentation from the IDocumentable.