Add custom signal handlers to arbitrate between Qt and SDL

Fixes #1496

app/streaming/session.h

@@ -103,6 +103,7 @@ public:
 
     Q_INVOKABLE bool initialize(QQuickWindow* qtWindow);
     Q_INVOKABLE void start();
+    Q_INVOKABLE void interrupt();
     Q_PROPERTY(QStringList launchWarnings MEMBER m_LaunchWarnings NOTIFY launchWarningsChanged);
 
     static