* change function signature:
mw.echo is loaded inside the mw.notification.overlay
The title of the overlay must be moved to mobile.startup as it renders
before this dependency is pulled down.
* Do not show a spinner for the mark all as read button for consistency
with the current rendering
* include the notification message string so the notification overlay can
be rendered without the mobile.notifications.overlay module

Bug: T217296
Change-Id: Id595b1158b86db9dc7725c8e3c0fb9cc35f49134