SW-826: adding Casacore.casa as dependency on LCS/Common makes many lofar libs...

SW-826: adding Casacore.casa as dependency on LCS/Common makes many lofar libs dependend on 3rd party libs which we don't actually use. This hinders us in deployment and maintenance on various systems. Hence, I removed the hard dependency on Casacore.casa, and made the empty-stub-CasaLogSink print out a warning message to cerr.

LCS/Common/src/CasaLogSink.cc

@@ -109,7 +109,7 @@ namespace LOFAR {
 #else
   void CasaLogSink::attach()
   {
-    cout << "WARNING: no casa logging available." << endl;
+    cerr << "WARNING: no casa logging available." << endl;
   }
 #endif