Show recently active media on smartspace signal

Smartspace will send an update when headphones are connected, but if the
user had recently active media (<3h) then we will show that media
instead of the smartspace cared. When smartspace later tries to expire
its card, this re-activated media will also be marked inactive again
(unless the user had started playback).

Fixes: 182811956
Fixes: 182813365
Test: manual
Test: atest com.android.systemui.media
Change-Id: I380f668c789c945d20814796607fcfc1e356de8f