Store model config at model directory

[tonyyang-svail]

After training, we need to store model config, such as model type, attribute values. Those values will be used to scanfold inference code.

[wangkuiyi]

Let us save all of them into the model table with sqlfs.

[wangkuiyi]

我感觉不应该把 SQLFlow 的相关信息放在 TenosrFlow 程序的 output directory 里。

[wangkuiyi]

我说的太绝对了。既然 TensorFlow model 是 SQLFlow model 的一部分，只要保证它们放在一起（在一个sqlfs table里）就行。