Implementing "LoadBalancing" plugin

[debbabi]

• if Node instance exists on the local Runtime Model:
  • it monitors the real node load, and update the "cpu" property of Node instance if exists.
• if Scope instance exists on the local Runtime Model:
  • it gets the cpu value of all the active nodes of the scope
  • it calculate the new meduim value
  • it activates or desactivates other nodes than the actual that host the scope instance.