Update settings for app hibernation

Created an preference in Apps & Notifcations page as the entry point for
apps that are hibernated. Also added a switch preference in AppInfo page
for users to exempt an app from hibernation.

Bug: 181172051
Test: HibernatedAppsPreferenceControllerTest;
HibernationSwitchPreferenceControllerTest;
AppInfoDashboardFragmentTest

Change-Id: I72a90ab391cd521150fc155a6d9c67c846b7360d