Use Signal's language for media preview timestamp

Fixes #3449
Closes #5600

// FREEBIE

src/org/thoughtcrime/securesms/MediaPreviewActivity.java

@@ -103,9 +103,7 @@ public class MediaPreviewActivity extends PassphraseRequiredActionBarActivity im
   private void initializeActionBar() {
     final CharSequence relativeTimeSpan;
     if (date > 0) {
-      relativeTimeSpan = DateUtils.getRelativeTimeSpanString(date,
-                                                             System.currentTimeMillis(),
-                                                             DateUtils.MINUTE_IN_MILLIS);
+      relativeTimeSpan = DateUtils.getExtendedRelativeTimeSpanString(this,dynamicLanguage.getCurrentLocale(),date);
     } else {
       relativeTimeSpan = null;
     }