I-2. Change the default number of Flow Messages in the flyout

Previously this was loading 25 unread notifications.  If less than 25 were
found it would add in 3 read notifications so it wasn't empty.

This patch changes things around to always return 25 notifications if the
user has at least that many.  Instead of backfilling a static count of 3
we backfill 25 - $count with previously read notifications.

Change-Id: I723316486216d7b9dacfcc9765c1a8212e973518
Merge "I-2. Change the default number of Flow Messages in the flyout"