Added icsneo_isOpen() functionality

include/icsneo/device/device.h

@@ -44,6 +44,7 @@ public:
 	virtual bool open();
 	virtual bool close();
 	virtual bool isOnline() const { return online; }
+	virtual bool isOpen() const { return opened; }
 	virtual bool goOnline();
 	virtual bool goOffline();
 
@@ -83,6 +84,7 @@ public:
 protected:
 	uint16_t productId = 0;
 	bool online = false;
+	bool opened = false;
 	int messagePollingCallbackID = 0;
 	int internalHandlerCallbackID = 0;
 	device_errorhandler_t err;