code: @Override
      public boolean applyAction(Model c) {
          if (c.getMapping().isOffline(node)) {
              c.getMapping().addOnlineNode(node);
              return true;
          }
          return false;
      }
docs: Put the node online on the model.
  
  @param c the model to alter
  @return {@code true} iff the node was offline and is now online