fix #262

lib/classes/JsonApi/Schemas/Activity.php

lib/classes/JsonApi/Schemas/BlubberComment.php

lib/classes/JsonApi/Schemas/BlubberThread.php

lib/classes/JsonApi/Schemas/ConsultationBlock.php

lib/classes/JsonApi/Schemas/ConsultationBooking.php

lib/classes/JsonApi/Schemas/ConsultationSlot.php

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

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

lib/classes/JsonApi/Schemas/FeedbackElement.php

lib/classes/JsonApi/Schemas/FeedbackEntry.php

lib/classes/JsonApi/Schemas/Institute.php

lib/classes/JsonApi/Schemas/Message.php

lib/classes/JsonApi/Schemas/SchemaProvider.php

lib/classes/JsonApi/Schemas/SemClass.php

lib/classes/JsonApi/Schemas/StatusGroup.php

lib/classes/JsonApi/Schemas/StudyArea.php

lib/classes/JsonApi/Schemas/User.php