New Features, still stucked with Dijkstra :(

-XML is saved only if there was a modification.
-Now it is imposbile to create an airport with empty strings for code or
city.
-All airports are loaded in combo boxes in the client dialog.
Done corrections
Used the now functioning dijkstra's shortest path
Graphics changes

-Now the user is shown the cost and the cheapest route.
-The involved nodes and Edges are highlighted.