feature: inflections in translations (specific distance_of_time...)

[fwolfst]

Hi
Probably related to #885 and #825 , in German you'd apply different cases for

Age: 3 hours
Alter: 3 Stunde

and

Created 3 hours ago
Vor 3 StundeN angelegt

The capitalized N is for illustrative purposes only.

distance_of_time_in_words and the related functions accept a translation-scope. If the rails-i18n gem would support 'cased' (inflected) translations and a convention for it, I could PR the German translations.

One candidate could be:

datetime:
    distance_in_words: # 'original'
      about_x_hours:
        one: etwa eine Stunde
        other: etwa %{count} Stunden
      inflected:
        dativ: # German case name
          about_x_hours:
            one: etwa einer Stunde # eineR
            other: etwa %{count} Stunden

or, more general, a variant scope with custom additions (apparently in hungarian you might want a past and future variant).