1.1.3dev: Tweak new preferences markup and CSS (refs #11853)
Append `-section` suffix to `id`s to avoid conflicts.
Use `h2` CSS similar to `.wikipage h2` from `wiki.css`, so `h2:target` from `trac.css` overrides `background` with yellow.

git-svn-id: http://trac.edgewall.org/intertrac/log:/trunk@13522 af82e41b-90c4-0310-8c96-b1721e28e2e2