Theorem is_submodule.smul_val

refactor(algebra/module): split of type constructions and move quotient, subtype and linear_map to their own theories in algebra/linear_algebra

refactor(algebra/module): rename submodule -> is_submodule, smul_left_distrib -> smul_add, smul_right_distrib -> add_smul, smul_sub_left_distrib -> smul_sub, sub_smul_right_distrib -> sub_smul