Added MenuBar and export to txt interface

Changelog:
Digrafo - Added getArista method which was really needed
GrafoPonderado - added getPeso method for the same reason as above
IOGrafo - added export to text capability and remove extension feature
JAristaDialog - added exception control
JVentana - All the interface has been revisited with menus and a list
Graph function has been enabled as well as a show all distances
feature.
App - removed just for debugging
Export2TXT - Added, jar to export to .txt files