show app icon badges over image notifications

[Danielle Foré]

Social apps (like chat, email, etc) send notifications with Avatars. That's great because it puts the focus on people, but I think it's still important to know just which app sent the notification so that you can respond in case the notification was dismissed before you could activate it.

To assist there, we should place a 24px app icon badge in the lower right corner of the icon area.

because I'm not sure this always makes sense (such as with Music notifications), we should probably still provide some kind of way (maybe through hints?) for clients to request that we don't display the badge.