play/pause button should hold the sound of a notification

[cm-t 🦄🏂🌈🎵]

When user has headset on, and there is a call phone, the user will naturally use the play/pause button built in the headset. And it just works :)

User might find natural to act the same way for other notifications incoming :

 * use headset
 * listen to music
 * alarm (set from clock app) is ringing (a loop ring)
 * the sound of the music is now low
 * the sound of the alarm ring is hight, and stressfull (because it is just happening, an alarm in the headset!, and possibly the sound chosen could naturally stressfull)
 * the user try to use the play/pause button
 * no effect
 * more stress
 * getting the phone out of the pocket/bag (optionally remove the headset)
 * tap the notification to stop the ring