Move push to talk bindings to overlaycontroller

The old system used the old OpenVR input system which is
incompatible with the new IVRInput.

This change broke the AccessbilityTabController, but
that is to be removed because the functionality can be
found elsewhere.

src/overlaycontroller.h

@@ -123,6 +123,9 @@ public: // I know it's an ugly hack to make them public to enable external
 private:
     QPoint getMousePositionForEvent( vr::VREvent_Mouse_t mouse );
     void processInputBindings();
+    void processMediaKeyBindings();
+    void processRoomBindings();
+    void processPushToTalkBindings();
 
 public:
     OverlayController( bool desktopMode, bool noSound, QQmlEngine& qmlEngine );