Localizable

Hello all !

In addition to my PR https://github.com/refinery/refinerycms-i18n/pull/51

I suggest this solution to add localized routes on refinerycms engine.

It will be great if the ActionDispatch::Routing::Mapper::localizable method will be directly added in refinerycms core to avoid duplicate code.

No need to fork route_translator with this solution :)

@parndt @simi