Replace the <p><br /></p> inserted between the toolbar and the preview area with...

Replace the <p><br /></p> inserted between the toolbar and the preview area with a ontop class. In shared.css we give this a bottom margin of 1em to add the space between the toolbar and preview.
As a bonus, because display: none; is now used when the preview area is not used, ajax/live previews actually get the spacing instead of it not showing up.
preview.js has also been tweaked to remove the display: none; when previewing.