more refactoring in names

include/centroidal-dynamics-lib/centroidal_dynamics.hh

include/centroidal-dynamics-lib/logger.hh

include/centroidal-dynamics-lib/solver_LP_abstract.hh

include/centroidal-dynamics-lib/solver_LP_clp.hh

include/centroidal-dynamics-lib/solver_LP_qpoases.hh

include/centroidal-dynamics-lib/util.hh

src/centroidal_dynamics.cpp

src/logger.cpp

src/solver_LP_abstract.cpp

src/solver_LP_clp.cpp

src/solver_LP_qpoases.cpp

src/util.cpp

test/test_LP_solvers.cpp

test/test_static_equilibrium.cpp