add OuputDevice as singleton to manage output to statusbar,

QtMeshViewer/Header/FileInterface.h

QtMeshViewer/Header/GeometryEngine.h

QtMeshViewer/Header/MshFile.h

QtMeshViewer/Header/OglViewerWidget.h

QtMeshViewer/Header/OutputDevice.h

QtMeshViewer/Source/GeometryEngine.cpp

QtMeshViewer/Source/MainWindow.cpp

QtMeshViewer/Source/MshFile.cpp

QtMeshViewer/Source/OglViewerWidget.cpp