Display’s a non-dismissable copy of the beta/media message in the footer after dismissing the standard message

- 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 
yeah - footer version has `is-hidden` by default.

if the message isn’t shown (e.g. it’s been dismissed before) then it just shows the footer version. if the message is  being shown, then mediator listens for a hide event to show the footer version.