Configuration validation

[dbu]

Trying to set up the LocaleBundle, i got this error page:

The service "lunetics_locale.allowed_locales_provider" has a dependency on a non-existent parameter "lunetics_locale.allowed_locales"

I guess this is not an optional thing, so we should change the configuration to make the option required, right? Or is the allowed_locales_provider only needed if i enable something else and in that sense semi-optional? then we should improve the DI class to detect the problem and give a better explanation of what is wrong.