Require browser notification permissions only when the user signs in

The only notification right now is for signed in users that are viewing
their room's page, so request permission only in this case.

app/assets/javascripts/shared.js.erb

@@ -68,5 +68,10 @@ var showNotification = function(title, options) {
   }
 };
 
-// TODO: only need permissions if the user is signed in
-Notification.requestPermission();
+// For now there are notifications only for users signed in and when they
+// are in their room's page
+$(document).on("turbolinks:load", function() {
+  if (GreenLight.user.roomOwner) {
+    Notification.requestPermission();
+  }
+});