Store each evaluation metrics as RDB field

[yuki-mt]

Motivation

Currently, evaluation result is stored as JSON string in result field in EvaluationResult model.
This makes it hard to control data by the metrics such as sorting EvaluationResult by precision.

Goal

Store each evaluation metrics as RDB field to make it easy to control data by the metrics

Implementation

TBD (precison, recall, fvalue can be list, so need to find a good solution to store them)