Add quit cli command and app quit option after stream session. Fixes #92 (#138)

* Add quit cli command and app quit option after stream session. Fixes #92

* Code review fixes.

app/streaming/session.h

@@ -30,6 +30,10 @@ public:
     int getDecoderCapabilities(StreamingPreferences::VideoDecoderSelection vds,
                                int videoFormat, int width, int height, int frameRate);
 
+    NvComputer* getComputer() const;
+
+    Q_INVOKABLE bool shouldQuitAppAfter() const;
+
 signals:
     void stageStarting(QString stage);