Merge pull request #847 from wenqing/uniq_solver_interface

Applications/CLI/ogs.cpp

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

Tests/MathLib/TestLinearSolver.cpp