clean up model usage (#8) * clean up model usage Signed-off-by: Lu Ken <bluewish.ken.lu@live.cn> * create model for Market Signed-off-by: Lu Ken <bluewish.ken.lu@live.cn> * add more model for restful API Signed-off-by: Lu Ken <bluewish.ken.lu@live.cn> --------- Signed-off-by: Lu Ken <bluewish.ken.lu@live.cn>