Stacked notifications for wear

[danybony]

I started working on adding stacked notifications to display multiple starred sessions for the same time slot.
The handheld notification will stay the same, with inbox style.
On wear every session will have its own notification with the following:

• Session title (as notification title)
• By speakers names
• In room name

Not sure if it will be useful to display also the starting time, as
"Starting in X minutes"

[alsutton]

Have you looked at the work Roman did as part of the L update? - google/iosched#45

[danybony]

I had a look at that, but Roman did it only for the feedback notifications, not for the ones fired when a session is about to start.
So we can improve that ;)