Improve launch time for app & notification screen

- We won't query recent apps in getAvailabilityStatus().
And then we do that in background thread.
So, we can launch app & notificatins screen as soon as possible.

- Create a RecentAppStatsMixin class which is responsible
for maintaining the recent apps data.

- Controllers and fragment update their UI after they got
onReloadDataCompleted callback from RecentAppStatsMixin.

Test: manual, robotest
Fixes: 128849426
Fixes: 126453868
Change-Id: I636d5878cb5d53496978fe613c625382d8d382bc