refs #187, asyncConnectTo method to avoid freeze when starting GUI/Core

* as discussed in https://dev.vatsim-germany.org/issues/187#change-1183
* using no longer connectTo() but asyncConnectTo() in constructor of simulator context
* changed Interface doxygen comments to copydoc

src/blackcore/context_simulator.h

@@ -62,6 +62,9 @@ namespace BlackCore
         //! \brief Connect to simulator
         virtual bool connectTo() = 0;
 
+        //! \brief Connect to simulator (asynchronous version)
+        virtual void asyncConnectTo() = 0;
+
         //! \brief Disconnect from simulator
         virtual bool disconnectFrom() = 0;