CrankNicolson → sixDoFSolver Relation

File in src/rigidBodyMotion/sixDoFRigidBodyMotion/sixDoFSolvers/CrankNicolson	Includes file in src/rigidBodyMotion/sixDoFRigidBodyMotion/sixDoFSolvers/sixDoFSolver
CrankNicolson.H	sixDoFSolver.H