Fix appearance and messages on demo page

Some 've-ui-toolbar-bar' classes hadn't been converted to OO.ui so the
toolbar had no border. Also removed a useless rule in mw.ViewPageTarget.css.

SA platform didn't override OO.ui.msg to use the ve.msg so no messages
were getting through.

Change-Id: Ieb5bc3c98d1c435ec194b201b517a688cd9b02b9
Merge "Fix appearance and messages on demo page"