Updating ItemInfo objects in the worker thread

> Launcher was making non-trivial updates to ItemInfo objects
on UI thread. These updates were getting skipped when the
Activity gets destroyed (possibly due to onConfigurationChange)
> Unregistering SessionCallback on application onTerminate,
rather than activity onDestroy

Bug: 17941096
Change-Id: Iad4a50871fe09470f26139b44a2e9886833032f1