Added a build flag for FSX specific code

FSX SimConnect code is build and linked only if enabled
by the build configuration.

refs #145

src/blackcore/blackcore.pro

@@ -37,12 +37,15 @@ DEFINES += LOG_IN_FILE
 HEADERS += *.h
 SOURCES += *.cpp
 
-HEADERS += $$PWD/fsx/*.h
-SOURCES += $$PWD/fsx/*.cpp
-
 win32 {
     HEADERS += $$PWD/win/*.h
     SOURCES += $$PWD/win/*.cpp
+
+    contains(BLACK_CONFIG, FSX) {
+        DEFINES += BLACK_WITH_FSX
+        HEADERS += $$PWD/fsx/*.h
+        SOURCES += $$PWD/fsx/*.cpp
+    }
 }
 
 win32:!win32-g++*: PRE_TARGETDEPS += ../../lib/blackmisc.lib ../../lib/blacksound.lib

src/blackcore/context_settings.h

@@ -34,6 +34,7 @@ namespace BlackCore
 
     public:
 
+        //! \brief Settings type
         enum SettingsType
         {
             SettingsHotKeys,

src/blackcore/context_simulator_impl.cpp

@@ -5,7 +5,10 @@
 
 #include "context_simulator_impl.h"
 #include "coreruntime.h"
-#include "fsx/simulator_fsx.h"
+
+#ifdef BLACK_WITH_FSX
+    #include "fsx/simulator_fsx.h"
+#endif
 
 using namespace BlackMisc;
 using namespace BlackMisc::PhysicalQuantities;
@@ -17,13 +20,17 @@ namespace BlackCore
     // Init this context
     CContextSimulator::CContextSimulator(QObject *parent) :
         IContextSimulator(parent),
-        m_simulator(new BlackCore::FSX::CSimulatorFSX(this)),
+        m_simulator(nullptr),
         m_updateTimer(nullptr),
         m_contextNetwork(nullptr)
-
     {
         m_updateTimer = new QTimer(this);
+
+#ifdef BLACK_WITH_FSX
+        m_simulator = new BlackCore::FSX::CSimulatorFSX(this);
         connect(m_simulator, &ISimulator::connectionChanged, this, &CContextSimulator::setConnectionStatus);
+#endif
+
         connect(m_updateTimer, &QTimer::timeout, this, &CContextSimulator::updateOwnAircraft);
     }
 
@@ -34,6 +41,9 @@ namespace BlackCore
 
     bool CContextSimulator::isConnected() const
     {
+        if (!m_simulator)
+            return false;
+
         return m_simulator->isConnected();
     }
 
@@ -44,6 +54,9 @@ namespace BlackCore
 
     void CContextSimulator::updateOwnAircraft()
     {
+        if (!m_simulator)
+            return;
+
         m_ownAircraft = m_simulator->getOwnAircraft();
 
         if (!m_contextNetwork)