Implement series first release date sorting

src/ui/collatable_container/collated_grid.rs

@@ -117,7 +117,7 @@ impl CollatedSeriesGrid {
 			SeriesProperty :: Name =>
 				series_1 . name . cmp ( & series_2 . name ) ,
 			SeriesProperty :: FirstReleaseDate =>
-				todo ! () ,
+				series_1 . first_release_date . cmp ( & series_2 . first_release_date ) ,
 		} ) ;
 		if sorting . direction == SortingDirection :: Descending { sorted . reverse () }