fix #889

app/controllers/course/courseware.php

app/views/course/courseware/index.php

app/views/course/courseware/tasks.php

lib/classes/JsonApi/Schemas/Courseware/Instance.php

resources/vue/components/courseware/ActivitiesApp.vue

resources/vue/courseware-activities-app.js

resources/vue/courseware-index-app.js

resources/vue/courseware-shelf-app.js

resources/vue/courseware-tasks-app.js

resources/vue/store/courseware/courseware-shelf.module.js

resources/vue/store/courseware/courseware.module.js