Data usage app labels, protect system, hide empty.

Derive better labels from PackageManager, including for sharedUid
case.  Disable "App settings" button when no ResolveInfo found, and
hide "Restrict" checkbox for system UIDs.  Also hide apps with 0
bytes usage.

Change-Id: I4b0a66f6912c02c56bfcbcb5b46f3ae2ba0df504