gvle: update the files management !!! SHOULD BE REBASED ON RONAN FIRST

- 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)