Use BaseLib::ConfigTree consistently.

Applications/ApplicationsLib/ProjectData.cpp

Applications/ApplicationsLib/ProjectData.h

Applications/CLI/ogs.cpp

BaseLib/ConfigTree.cpp

BaseLib/ConfigTree.h

FileIO/XmlIO/Boost/BoostXmlGmlInterface.cpp

FileIO/XmlIO/Boost/BoostXmlGmlInterface.h

MathLib/LinAlg/Eigen/EigenLinearSolver.cpp

MathLib/LinAlg/Eigen/EigenLinearSolver.h

MathLib/LinAlg/EigenLis/EigenLisLinearSolver.cpp

MathLib/LinAlg/EigenLis/EigenLisLinearSolver.h

MathLib/LinAlg/Lis/LisLinearSolver.cpp

MathLib/LinAlg/Lis/LisLinearSolver.h

MathLib/LinAlg/PETSc/PETScLinearSolver.cpp

MathLib/LinAlg/PETSc/PETScLinearSolver.h

MathLib/LinAlg/Solvers/GaussAlgorithm-impl.h

MathLib/LinAlg/Solvers/GaussAlgorithm.h

NumLib/TimeStepping/Algorithms/FixedTimeStepping.cpp

NumLib/TimeStepping/Algorithms/FixedTimeStepping.h

ProcessLib/GroundwaterFlowProcess.h