apvlv: copy main_menubar.glade to out dir

The application requires the main_menubar.glade alongside the
Startup.pdf. Just making sure all required assets are present 😉.

Currently `apvlv` fails with the `(apvlv:16999): Gtk-ERROR **: failed to add UI: Failed to open file '${store-path}-apvlv-0.1.5/share/doc/apvlv/main_menubar.glade': No such file or directory
zsh: trace trap  apvlv` error.

pkgs/applications/misc/apvlv/default.nix

@@ -41,6 +41,7 @@ stdenv.mkDerivation rec {
     # displays pdfStartup.pdf as default pdf entry
     mkdir -p $out/share/doc/apvlv/
     cp ../Startup.pdf $out/share/doc/apvlv/Startup.pdf
+    cp ../main_menubar.glade $out/share/doc/apvlv/main_menubar.glade
   '';
 
   meta = with stdenv.lib; {