Extract common #setup/#teardown from subclasses of TestRemoteDatabase
Reflect Padrino settings about database to test environment
Remove option same to the default
Change namespace of Padrino app: Epub -> EPUBSearcher

Reasons are:

* `Epub` is too general. It might be used by ActiveRecord model class or so on.
* It becomes easy to access to lib classes such like `RemoteDatabase` from
  Padrino application