Show "App Center" in Gnome Shell activities view

Currently, the window in the Activities view in Gnome Shell has
"snap-store" as its name, which is incorrect because this is the
brand-new "App Center". The reason is that the Activities view
shows the window title, but the app center doesn't set it, so
it is set to the binary name.

This patch fixes it, although it should be modified in the future
to use the translated name.

fix ubuntu#1425

packages/app_center/linux/my_application.cc

@@ -33,6 +33,7 @@ static void my_application_activate(GApplication* application) {
 
   GtkWindow* window = GTK_WINDOW(hdy_application_window_new());
   gtk_window_set_application(window, GTK_APPLICATION(application));
+  gtk_window_set_title(window, "App Center");
 
   GdkGeometry geometry;