Add new property for customizing the defaultEnumTypeHandler

[kazuki43zoo]

Related with gh-440

By this change, we can customize a default enum type handler as follow:

@Bean
SqlSessionFactoryBean sqlSessionFactory(DataSource dataSource) {
  SqlSessionFactoryBean factoryBean = new SqlSessionFactoryBean();
  factoryBean.setDataSource(dataSource);
  factoryBean.setDefaultEnumTypeHandler(EnumOrdinalTypeHandler.class); // new property
  return factoryBean;
}