Bug 1110966 - EOY fundraising home page takeover

Still somewhat in progress and I haven't added the waffle switch yet, but I wanted to kick off review. I think my JS for changing the form action is probably fairly hacky; I'd be very open to suggestions for a better approach.
Is all this still required to use an l10n tag? I think it can be simplified now - certainly the `settings.DEV` part is no longer required I think.