Prepare EigenvalueSolver to incoming use of Eigen3

src/algebra/CMakeLists.txt

src/algebra/EigenvalueSolver.cpp

src/algebra/EigenvalueSolver.hpp

src/algebra/EigenvalueSolverOptions.cpp

src/algebra/EigenvalueSolverOptions.hpp

src/language/modules/LinearSolverModule.cpp

src/utils/checkpointing/Checkpoint.cpp

src/utils/checkpointing/EigenvalueSolverOptionsHFType.hpp

src/utils/checkpointing/LinearSolverOptionsHFType.hpp

src/utils/checkpointing/Resume.cpp

tests/test_EigenvalueSolver.cpp

tests/test_LinearSolverOptions.cpp

tests/test_checkpointing_HFTypes.cpp