Support outline view in the HTML export

Users should be able to select Outline view in the HTML export, including the inline display of topic notes.

This would make the HTML export more suitable for linear documents. It would also be better suited to the built-in Web browser in MindManager than the map view.

A linear export was available in the deprecated Web export feature, although this generated a HTML page with associated files rather than a single HTML5 file with everything embedded.