-added EmptySystem supprort (called once per frame, sholud be once per jobs)

-EntitiesData can contain "thread_id" which is filled with ID of current thread

source/ecs/system.d

@@ -94,6 +94,8 @@ package:
     bool m_execute = true;
     ///system id
     ushort m_id;
+    ///is system empty? Empty systems don't update entities, and is called once per update
+    bool m_empty = false;
 
     ///should system update and catch events?
     bool m_enabled = false;