Adds EchoEventPresentationModel::canRender() for notification types to
indicate that something can't be rendered if for example, a page is
deleted.
In that case, the notification is marked as read in a deferred update.
All callers were also updated to check if the notification was formatted
properly.
Bug: T116888
Change-Id: Idb975feaec893ef86c41cc487102e3539c07e328
Push the $wgEchoNotifications dependency to
NotificationFormatter::factory(), and only catch exceptions we're
actually expecting (NotificationFormatter::format()).
And clean up the logging to use structured logging while we're at it.
Change-Id: I7e18c318c5c81b6a38e55f27ef8f604654f10858
