Grammar cases are not handled correctly for $time / `$time ago` / `in $time`

[jacobras]

Issues in the following languages:

• German
• Polish
• Russian

Fix:

• Duration should be nominative, which it currently is.
• $time ago should be dative for German, but accusative for Russian and nominative for Polish.
• in $time should be dative for German, but accusative for Russian and accusative for Polish.

Should also check other languages. Might be simplest (in terms of maintaining languages) to replace the separation of duration/phrase with phrases only. For example, strings for "seconds_duration" and "seconds_ago" and "in_seconds".