Don't load the admin's locales unless you explicity register the admin
module.

If you're using `Padrino::Admin::AccessControl`, the extension
`Padrino::Admin` gets registered for you. Otherwise, if you want to use
the locales you have to add `register Padrino::Admin` to your
`app/app.rb`.
Remove assertions for orm locale
Merge pull request #1702 from padrino/rework-admin-locales

Don't load the admin's locales unless you explicity register the admin module and remove AR version of locales