[DBClientConfig] Rename the file to DBTablesConfig.

This patch only renames the (source and header) file name.
The change of the class name will be soon after.
[DBClientConfig] Rename the class name to DBTableConfig.

The DBClient's sub class is a set of tables in a DB.
So the new directly expresses that.
Merge pull request #396 from project-hatohol/rename-dbtables-config

Rename dbtables config