Add datetime function to subscriptions feed local database sorting

These entities were being sorted by date_published, and it works as long as they are inserted with the same timezone. This solution is weak, because if the timezone ever changes among entities the sorting will stop working. Using datetime function solves this issue.

WordPress/src/main/java/org/wordpress/android/datasets/ReaderPostTable.java

@@ -745,7 +745,7 @@ private static String getSortColumnForTag(ReaderTag tag) {
         if (tag.isPostsILike()) {
             return "datetime(date_liked)";
         } else if (tag.isFollowedSites()) {
-            return "date_published";
+            return "datetime(date_published)";
         } else if (tag.tagType == ReaderTagType.SEARCH) {
             return "score";
         } else if (tag.isTagTopic() || tag.isBookmarked()) {