refs #382, reviewed audio context handling

* only init QDbusServer for P2P
* changed init order of contexts in runtime
* use "fake" signal to call setComVoiceRooms (remote in GUI)
* added slot to change voice room callsign
* used "org.swift" instead of "net.vatim" (just style)
* used const QString for serviceName
* added correct copyright header (just style)

src/blackcore/context_audio_empty.h

@@ -59,6 +59,13 @@ namespace BlackCore
             logEmptyContextWarning(Q_FUNC_INFO);
         }
 
+        //! \copydoc IContextAudio::setOwnCallsignForRooms
+        virtual void setOwnCallsignForRooms(const BlackMisc::Aviation::CCallsign &callsign) override
+        {
+            Q_UNUSED(callsign);
+            logEmptyContextWarning(Q_FUNC_INFO);
+        }
+
         //! \copydoc IContextAudio::getRoomCallsigns()
         virtual BlackMisc::Aviation::CCallsignList getRoomCallsigns(int comUnitValue) const override
         {