intro/discovery/discovery rid out of Xorm

[logrusorgru]

The xorm drops (*xorm.Rows).Next() error and (*xorm.Rows).Err() can only returns sql.ErrNoRows. Since, CXO have a little SLQ work, then I think CXO should rid out of the xorm to

• avoid unnecessary dependency
• handle possible error

The work is faster then time of waiting reply from xorm developers.

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Work: 50% (in progress, next after #147) Test: 0%