Pin ‘banner’ messages to footer once they’ve been dismissed

- messages broadcast a `’message:hidden:messageId` event when dismissed
- media & beta messages are shown in the footer once dismissed
- media & beta messages reordered slightly, to avoid unnecessary string concatenation 
As you have repeated both of these class names twice in the file, its good convention to store in a `var` or  `cls` object to prevent repetition and be more DRY.