Allow user to interact with running timers from notifications.

Bug: 22376599

Timer in use collapsed notification now offers the following actions:
for single running timer: pause, +1
for single paused timer: resume, reset
for multiple timers (paused and/or running): reset all

Additionally, clicking the notification now scrolls the user to an
active timer in TimerFragment.

Change-Id: I9e2385c7601c80387bebc144f6fc281786e3b3f2