gvle: update the files management

- The dialog used to start a new project has been removed. Now we use a
  regular file dialog. It does enable to choose a directory anywhere, to
  be the recipient of a package.
- The Global VPZ features have been removed.
- The regular file chooser dialog is used to open a vpz file, and the
  older vpz chooser dialog has been removed.
(closes #82)