Allow blog, blogpost and textbox blocktypes having links or manually created <img> tags to artefacts to have those artefacts counted as being within the blocktype, and thus within the view.

This is so if people manually link to or source artefacts within textual content, those artefacts will be downloadable when the view is shown to others.

Not backporting to 1.0 although the problem will most certainly exist there - the patch is just too big to trust on a stable release.