add tag task and varioius cleanup

lib/tasks/make_task.js

@@ -42,6 +42,9 @@ function makeTask(logger, obj) {
     case TaskName.Redirect:
       const TaskRedirect = require('./redirect');
       return new TaskRedirect(logger, data);
+    case TaskName.Tag:
+      const TaskTag = require('./tag');
+      return new TaskTag(logger, data);
   }
 
   // should never reach