Can get older posts on latest posts page

lib/lists/posts_list.dart

@@ -46,4 +46,12 @@ class PostsList extends ListBase<Post> {
 
     return set;
   }
+
+  /// Get the ID of the oldest post of this list. Returns 0 if the list is empty
+  int get oldestID {
+    if(isEmpty)
+      return 0;
+
+    return this.elementAt(length - 1).id;
+  }
 }