[server][ColumnDef] Remove ColumnDef::tableName

In https://github.com/project-hatohol/hatohol/pull/404#issuecomment-52587661, we have a concensus about removing `ColumnDef::tableName`. This pull request does it. See each commit message for details.
OK!
I've added it.

Another codes in this file should be also fixed in another pull request.