Revision 2051

Make Thuban remember path selections (at least for one application run).

* Thuban/UI/application.py (Application.OnInit): Initialize path as a
	attribute of application object. Path is a dictionary of
	strings, currently with the items "data" and "projection".
	(Application.SetPath): New, stores path for the specified item.
	(Application.Path): New, return path for the specified item.

* Thuban/UI/mainwindow.py
	(MainWindow.OpenSession, MainWindow.SaveSessionAs,
	MainWindow.AddLayer, MainWindow.AddRasterLayer,
	MainWindow.TableOpen): Access "data" path information of the
	application.

* Thuban/UI/projdialog.py (ProjFrame._OnImport, ProjFrame._OnExport):
	Access "projection" path information of the application.