Extracted solver creation

src/elasticity/MainElasticity.cpp

src/elasticity/MainElasticity.hpp

src/elasticity/solvers/CMakeLists.txt

src/elasticity/solvers/DynamicMechanicsSolver.cpp

src/elasticity/solvers/DynamicMechanicsSolver.hpp

src/elasticity/solvers/ElasticitySolver.cpp

src/elasticity/solvers/ElasticitySolver.hpp

src/elasticity/solvers/IterativePressureSolver.cpp