[src-psale] 'Reia lucru' with preview

It would be nice to have a **GtkSourceView** widget as a preview widget for the 'Reia lucru' button in the 'fcod' moule. This would make the selection process easier.

A good starting point might be the ![GtkFileChooser::gtk_file_chooser_set_preview_widget](http://developer.gnome.org/gtk/stable/GtkFileChooser.html#gtk-file-chooser-set-preview-widget) function.
