Don't launch activities from statusbar if running

Added FLAG_ACTIVITY_SINGLE_TOP when starting activities launched
from the StatusBar.  If the activity is already running
at the top of the history stack, then don't relaunch.

Fixes: 77335366
Test: manual (click "Manage notifications" from notification shade,
then trigger it again - no issues)

Change-Id: I2e9ce2c57544c3066dc4fa0cc9662f0aa85565ab