Improve launch time for Apps & notifications page

In original design, we reload usage data at least thrice
for showing recent apps.

For now, we only reload usage data once in constuctor.
And we reload data again when we are calling updateState.

Test: Open App & notifications page, and then I compare the lauch time
with P platform device.
Fixes: 126013076

Change-Id: Ida769f28a4419125e1948e36658686ee55bf51a5