Show message when no apps/permissions are allowed/denied.

Instead of showing an empty allowed/denied header, we now show a
message saying that nothing is there.

Change-Id: I6e8ccd31c4af9f9ef6a0f699bc91fd7fd732e52b
Fixes: 120675937
Test: See messages when no apps/permissions are allowed/denied.
Test: Ensure message appears/disappears as I toggle permissions.