Create function to know if a user has a submission.

classes/submission.py

@@ -234,6 +234,18 @@ class SubmissionMap:
         """
         return self._submission_map[user_id]
 
+    def has_user(self, user_id: int) -> bool:
+        """
+        Tells if user has an active submission in submission map.
+
+        Args:
+            user_id (int): user id
+
+        Returns:
+            bool: bool indicating if user id is in submission map
+        """
+        return user_id in self._submission_map
+
     def remove_user_submission(self, user_id: int) -> None:
         """
         Removes a user's Submission. Use when Submission is complete.