Delay setting the DBusConnection for a DBusObject

Previously, the DBusconnection had to be set at construction time and could
not be changed over the DBusObject life time. Now a new connection can be
set anytime and as often as required.
The shared ownership is now also properly implemented by shared pointers.

ref T291

src/xswiftbus/service.h

@@ -39,7 +39,7 @@ namespace XSwiftBus
     {
     public:
         //! Constructor
-        CService(CDBusConnection *connection);
+        CService();
 
         //! Destructor
         ~CService() override = default;