V1 database records fixes

[allenwq]

Because of the lacking of foreign_key constraint, some of the records are not valid but still stores in db, to fix:

• Add null: false to question_assessments, question_id and assessment_id, there are question_assessments with nil assessment_id
• Handle question_assessments with deleted_assessments
• Tag and Tag group id inconsistent, probably can be fixed by:

Tag set course_id same as tag_group course_id
# Tag.where(course_id: nil).each { |t| id = t.tag_group.course_id; t.update_column(:course_id, id)}

• Tag and Taggable in different courses. Should drop the taggable instead.

• Drop answers with null submission and question, add null: false

• inconsistent folders (folders and subfolder belong to differernt course)

def fix_course_id(folder, course_id)
  return if folder.nil?

  if folder.course_id != course_id
    puts "Update folder #{folder.name} #{folder.id} to course #{course_id}, origin: #{folder.course_id}"
    folder.update_column(:course_id, course_id)
  end

  folder.subfolders.each { |f| fix_course_id(f, course_id) }
end