app: turn the input devices dialog into a session managed toplevel

It works exactly as the keyboard shortcuts dialog now and has its own
menu entry: Edit -> Input Devices.

app/dialogs/input-devices-dialog.h

@@ -0,0 +1,25 @@
+/* GIMP - The GNU Image Manipulation Program
+ * Copyright (C) 1995 Spencer Kimball and Peter Mattis
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef __INPUT_DEVICES_DIALOG_H__
+#define __INPUT_DEVICES_DIALOG_H__
+
+
+GtkWidget * input_devices_dialog_new (Gimp *gimp);
+
+
+#endif /* __INPUT_DEVICES_DIALOG_H__ */