The figure and figure caption should not be part of the editable content

Currently, the figure macro puts the FigureBlock inside its editable content and the figure caption puts the FigureCaptionBlock inside its editable content. This is currently not an issue because the XHTML 1.0 renderer that we use for editing doesn't produce any output for them but with CKEDITOR-207 and XRENDERING-627 where we will switch to HTML5 and actually parse these tags this will become an issue. The obvious fix of putting the figure outside the metadata block works but has the consequence that the metadata block of the caption is now inline content and no longer editable due to limitations of CKEditor, see CKEDITOR-199.