Prefer GtkFileChooserNative over GtkFileChooser

[JoostvanPinxten]

Especially on Windows, the Gtk File Chooser looks very different, and does not have all the functionality that I expect to have.

Therefore, I would appreciate (a setting) to use the GtkFileChooserNative, class instead which will fall back to the current one if no native file chooser is available.

[kees-jan]

Sounds good. Would it be possible for you to do a pull-request? ;-)

[JoostvanPinxten]

Yes, I have that intention. However, I am quite stretched for time. Will do this once the SepGroup8 delivers their changes, as to not conflict with those.