feat: add open questions with a pending grading state

- migration: open question type, rubric, max_length, quiz grader and
  the grading and review columns of attempt answers
- open answers are checked, stored as pending and never scored on
  answer; a changed text resets the grading state
- student JSON gains text, grading_status, grader_feedback,
  review_comment, max_length, needs_review and open_answers; the
  rubric is never serialized

lang/en/lang.yaml

@@ -15,6 +15,10 @@ api:
     attempt_limit_reached: All attempts at this test have been used.
     answer_locked: An answer in this test cannot be changed.
     category_not_allowed: A test covers the whole quiz; a category cannot be chosen.
+    text_required: Write an answer to this question.
+    text_too_long: The answer is longer than this question allows.
+graders:
+    manual: Manual (the owner grades)
 permissions:
     access_quizzes: Manage quizzes, questions and answers
     access_attempts: View quiz attempts

lang/pl/lang.yaml

@@ -15,6 +15,10 @@ api:
     attempt_limit_reached: Wykorzystano już wszystkie podejścia do tego testu.
     answer_locked: W tym teście nie można zmienić udzielonej odpowiedzi.
     category_not_allowed: Test obejmuje cały quiz; nie można wybrać kategorii.
+    text_required: Wpisz odpowiedź na to pytanie.
+    text_too_long: Odpowiedź jest dłuższa, niż pozwala to pytanie.
+graders:
+    manual: Ręcznie (ocenia właściciel)
 permissions:
     access_quizzes: Zarządzanie quizami, pytaniami i odpowiedziami
     access_attempts: Podgląd podejść do quizów