Updated code to use a common base class and single factory pattern.

Implementation of Operator classes using dynamic polymorphism.

LibUtilities/ErrorUtil.cpp

+#include "ErrorUtil.hpp"
+
+namespace Nektar
+{
+    std::ostream *ErrorUtil::m_outStream = &std::cerr;
+    bool ErrorUtil::m_printBacktrace     = true;
+}
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