Support GNotification

It's used if there's a gtk notification daemon or application is running sandboxed without access to the freedesktop protocol.

GNotification API is poor, but should feel native on environments using GNOME technologies.

Telegram/SourceFiles/platform/platform_specific.h

@@ -7,8 +7,20 @@ https://github.com/telegramdesktop/tdesktop/blob/master/LEGAL
 */
 #pragma once
 
+namespace base::options {
+
+template <typename Type>
+class option;
+
+using toggle = option<bool>;
+
+} // namespace base::options
+
 namespace Platform {
 
+extern const char kOptionGApplication[];
+extern base::options::toggle OptionGApplication;
+
 void start();
 void finish();