Use CApplication::isNetworkAccessible() wherever possible

Up to now we had a mixture of different methods to detect whether
network is connected, accessible or both. Even if they implied a
different meaning, they were all doing the same and internally
referred to almost the same code. Almost, since our implementation
of CNetworkUtils::hasConnectedInterface refers to code from Qt 4.4.
However, all of them returned a boolean status whether a network
interface is generally up or not. Instead of maintaining our own
version, use Qt functions.

refs #869

src/blackcore/setupreader.cpp

@@ -197,7 +197,7 @@ namespace BlackCore
     CStatusMessageList CSetupReader::triggerReadSetup()
     {
         if (this->m_shutdown) { return CStatusMessage(this, CStatusMessage::SeverityError, "shutdown"); }
-        if (!CNetworkUtils::hasConnectedInterface())
+        if (!sApp->isNetworkAccessible())
         {
             const CStatusMessage m(this, CStatusMessage::SeverityError,
                                    "No network, cancelled reading of setup");