Add sending queue status to help page

[MAILPOET-1459]

lib/Models/ScheduledTask.php

@@ -11,6 +11,7 @@ class ScheduledTask extends Model {
   const STATUS_COMPLETED = 'completed';
   const STATUS_SCHEDULED = 'scheduled';
   const STATUS_PAUSED = 'paused';
+  const VIRTUAL_STATUS_RUNNING = 'running'; // For historical reasons this is stored as null in DB
   const PRIORITY_HIGH = 1;
   const PRIORITY_MEDIUM = 5;
   const PRIORITY_LOW = 10;