Toolbar: Modified deprecation comment.

buttonMarkup() has been deprecated as well so you have to classes
instead the data-role. Also made clear that you have to add the button
position classes yourself. See
https://github.com/jquery/jquery-mobile/issues/5933
Demos: Added custom style for h3 headings.
Demos: Small change in default demo page.
Demos: Updated all toolbar demo pages.
Demos: added note to FAQ pages that they are not updated.