Bundle new-topic notifications

Better would be to teach Echo how to bundle things in different ways, but for
now this is a reasonable first step.

Currently bundled output messages are only enabled when more than one
user triggeres those events.  This works great for messages like:

    User X posts on your talk page

When the bundle would say:

    User X and 0 others posted on your talk page

But bundled messages that display a count of events, like:

    N new topics were posted to X

will want to use the bundled messaging any time the event count
is > 1, regardless of the number of users performing the event.

This patch makes the flow-new-topic notifications use the second method.
(cherry picked from I3e95d82d5e5ee8f896b53082ec2bbd309c5681f5 )

Change-Id: I43756fbd4134439446f1bb9c17ccab88202159ba
Merge "Bundle new-topic notifications" into wmf/1.24wmf20