Add app for Facebook tabs and apps.
Add initial Download Firefox Facebook tab template.
Display latest Firefox version in Download Tab
Add decorators argument to `mozorg.utils.page`

The `decorators` argument can be a reference to a single decorator or an iterable object of decorators to be applied to the given template. It's an optional parameter so existing calls to `page` should continue to work without incident.

The decorators are applied in reverse order to match the behavior of the other techniques for applying decorators (nested decorator function calls on the view function and the `@` operator).
Allow Download Tab to be displayed in iframes