refactored plugins to use std::string

Common/Options.cpp

Fltk/FlGui.cpp

Fltk/pluginWindow.cpp

Parser/Gmsh.tab.cpp

Parser/Gmsh.y

Plugin/Annotate.cpp

Plugin/Annotate.h

Plugin/Curl.cpp

Plugin/Curl.h

Plugin/CutGrid.cpp

Plugin/CutGrid.h

Plugin/CutMap.cpp

Plugin/CutMap.h

Plugin/CutParametric.cpp

Plugin/CutParametric.h

Plugin/CutPlane.cpp

Plugin/CutPlane.h

Plugin/CutSphere.cpp

Plugin/CutSphere.h

Plugin/Divergence.cpp