doc_layout : fixed comments, delete useless classes and improve DocListElement

Signed-off-by: Maxime Leroy <maxime.leroy76@gmail.com>
nitdoc : fixed sidebar html generation on overview and module page

fixed with the new doc_layout, whitout useless classes like DocListElementFull,
DocListElementSpan and DocListElementLink

Signed-off-by: Maxime Leroy <maxime.leroy76@gmail.com>