implement translation behavior default locale

Unless explicitly overriden, the behavior now reads I18n::defaultLocale() to find the locale to return translations in.

Bundled with this change set is adding support to the translate behavior
for unhydrated result sets

Closes #4509

Ref #4660 
What if I want my defaultLocale to be `fr_FR` wouldn't this mean I have to call `->config('defaultLocale') for all models? Maybe setting `defaultLocale` to `I18n::defaultLocale()` in the constructor would be better.