Remove placeholder logs of notifications sent

From the:
- dashboard
- activity page

This info will be confusing for users at the hack day, because it will say
they’ve already sent messages when they first sign up.

This involved changing the table macro to have a nice ‘no rows’ message.

tests/app/main/views/test_dashboard.py

@@ -13,5 +13,4 @@ def test_should_show_recent_jobs_on_dashboard(app_,
             response = client.get(url_for('main.service_dashboard', service_id=123))
 
         assert response.status_code == 200
-        assert 'Test message 1' in response.get_data(as_text=True)
-        assert 'Asdfgg' in response.get_data(as_text=True)
+        assert 'You haven’t sent any text messages yet' in response.get_data(as_text=True)