Fixed bug renaming place, added status_var to mainWindow, finished expandNet integration.

-> Fixed bug when opening-renaming-saving-renaming a node.
  '-> When a node is renamed, the arc objects are destroyed and built again.
      When being destroyed, the xml node is also deleted, so when saving (and building a new xml node)
      the arcs should update the _treeElement field with the id of the newly created xml node.
-> Added status_var to mainWindow
  '-> Added the variable for when there is no tab open.
  '-> Added messages of saved and open with the save and open functions, to be displayed in the status_bar.
  '-> Made the status bar span through all width of the window.
-> Finished expandNet integration.
  '-> Added a fileDialog to specify where to save the created file.
  '-> Added lines to fill the AvailableModels files with the RunningConditions and the DesiredEffects fields (for action models).
  '-> Added lines to remove the tmp_dir completely.