[server] DBTermCodec breaks the abstraction of DB access

[kz0817]

Access to DBs is abstracted by DBClient and its subclasses. So users of their classes don't have to take into account DB's details. However, DBTermCodec was added to generate a part of a where clause in an SQL statement that dependent on a DB in HostResourceQueryOption.
Although it hides some details of DBs, the existence is ugly. That kind of operation should be perfumed in a DBClient layer by right.

[a24-yamaguchi]

Hatohol16.12で実装できないので、マイルストーンを削除。