Use notification counts (instead of assuming all 1)

We still ignore group summary headers, which means, for example,
we won't get Gmail unread count. But single notifications that
have numbers associated, such as messages from a single contact
will be included in the badge count. So if you have 2 hangounts
threads, one with 10 messages and one with 8, the badge would
say 18.

Bug: 34939841
Change-Id: I20b9a857d91715e10c0da400a1cee209d7b837b8