i18n fallback fix

this allows
- `be` to fallback to `be-BY`   (belerusian)
- `pt` to fallback to `pt-BR`   (portugeuse)

the solution comprises a few parts:
- adding a stub `fallback.be.yml` so that i18n auto-includes `be` in `available_locales`
- adding a constant to the locales_helper to track fallback locales
- adding switch in the method `locale_name` so that `be` knows what to call itself and doesn't just offer ` see this website in ------ `  in frontpage locale banner

this last one could be done differently, open for feedback
Na. I would WAY rather we had two be options in the drop down, than carried
this complexity into the system. Please do it that way.


On Fri, Sep 5, 2014 at 10:48 AM, mix irving <notifications@github.com>
wrote:

> In app/helpers/locales_helper.rb:
>
> >
> >    def locale_name(locale)
> > -    LANGUAGES.key(locale.to_sym)
> > +    locale = replace_fallback_locales(locale)
>
> I've made this logic a little less verbose. Does that help allay your
> concerns?
>
> def replace_fallback_locales(locale)
>    Loomio::I18n::LOCALE_FALLBACKS[locale.to_sym] || localeend
>
> —
> Reply to this email directly or view it on GitHub
> <https://github.com/loomio/loomio/pull/1644/files#r17147705>.
>