GUI can now be compiled without the mesh module

CMakeLists.txt

src/common/GmshGlobal.cpp

src/fltk/FlGui.cpp

src/fltk/classificationEditor.cpp

src/fltk/classificationEditor.h

src/fltk/fieldWindow.cpp

src/fltk/graphicWindow.cpp

src/fltk/highOrderToolsWindow.cpp

src/fltk/partitionDialog.cpp

src/fltk/statisticsWindow.cpp

src/fltk/touchBar.mm

src/fltk/viewButton.cpp

src/geo/GFace.cpp

src/geo/scriptStringInterface.cpp