Add an 'Update your OS' top bar.

Set EOL for Windows XP / Vista version at September 1, 2019.

Telegram/SourceFiles/platform/linux/info_linux.cpp

@@ -32,4 +32,8 @@ QString SystemLanguage() {
 	return QString();
 }
 
+QDate WhenSystemBecomesOutdated() {
+	return QDate();
+}
+
 } // namespace Platform