* src/main.cc (main): Use gtk_window_set_default_icon_name() to
have the default window icon looked up in the icon theme, rather
than explicitely specifying an image filename.  For some reason
this method has not been wrapped yet.
(set_default_window_icon): Remove now unused function.
* src/aboutdialog.cc (AboutDialog::create): For the same reason as
above, use Gtk::Image::set_icon_from_name() instead of an explicit
filename to load the application icon.
* src/globalstrings.h (application_icon_filename): Remove now
unused string.