Redirect all controllers to login if required

We want to skip the filter for sessions controller so that we can login
and we want to skip the filter for static pages because those should be
visible to visitors.

spec/controllers/topics_controller_spec.rb

@@ -435,6 +435,25 @@ describe TopicsController do
 
     end
 
+    context "when 'login required' site setting has been enabled" do
+      before { SiteSetting.stubs(:login_required?).returns(true) }
+
+      context 'and the user is logged in' do
+        before { log_in(:coding_horror) }
+
+        it 'shows the topic' do
+          get :show, topic_id: topic.id, slug: topic.slug
+          expect(response).to be_successful
+        end
+      end
+
+      context 'and the user is not logged in' do
+        it 'redirects to the login page' do
+          get :show, topic_id: topic.id, slug: topic.slug
+          expect(response).to redirect_to login_path
+        end
+      end
+    end
   end
 
   describe '#feed' do