Add datetime function to Saved feed local database sorting

	These entities were being sorted by date_tagged as a string, 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

@@ -749,7 +749,7 @@ private static String getSortColumnForTag(ReaderTag tag) {
         } else if (tag.tagType == ReaderTagType.SEARCH) {
             return "score";
         } else if (tag.isTagTopic() || tag.isBookmarked()) {
-            return "date_tagged";
+            return "datetime(date_tagged)";
         } else {
             return "datetime(date_published)";
         }