When trying to reply without signing in, show warning.

This is a workaround, until we can get the forced
log-in workflow properly working for these cases.

Closes #364.

h/js/controllers.coffee

@@ -566,7 +566,7 @@ class Annotation
     $scope.reply = ($event) ->
       $event?.stopPropagation()
       unless annotator.plugins.Auth? and annotator.plugins.Auth.haveValidToken()
-        $scope.$emit 'showAuth', true
+        $window.alert "In order to reply, you need to sign in."
         return
 
       references =