Implement windows 8.1+ notifications

This splits notifications up into multiple backends
currently only libnotify on unix and win8 toasts.

The win8 backend was originally written by @leeter
though heavily modified.

src/fe-gtk/notifications/notification-dummy.c

@@ -0,0 +1,39 @@
+/* HexChat
+ * Copyright (C) 2015 Patrick Griffis.
+ *
+ * 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 2 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, write to the Free Software
+ * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA
+ */
+
+void
+notification_backend_show (const char *title, const char *text, int timeout)
+{
+}
+
+int
+notification_backend_init (void)
+{
+	return 0;
+}
+
+void
+notification_backend_deinit (void)
+{
+}
+
+int
+notification_backend_supported (void)
+{
+	return 0;
+}