Fix:
  * Nodes are inserted at the correct position.
  * When n' ,a successor of n, has an ID lower than the ID of n, n' is inserted at the end of the fingers table.

Other:
  * Unit tests have been completely rewritten.
  * ChordActor's logic have been separate from linkActor's logic.
  * ChordActor have it's own tests.
  * Local ChordActor with it's own main class.
  * Network location has been splitted in an interface and an empty class (for testing purpose).