feat: bidirectional communication (planning#460)

Makefile

README.md

functions/pagination-response.js

notes-for-rueckkanal-doku.txt

spec/callbacks/case-closure-announcement.yaml

spec/callbacks/new-events.yaml

spec/callbacks/new-replies.yaml

spec/callbacks/new-submissions.yaml

spec/endpoints/attachments/uuid.yaml

spec/endpoints/cases/events/index.yaml

spec/endpoints/cases/index.yaml

spec/endpoints/cases/uuid.yaml

spec/endpoints/destinations/index.yaml

spec/endpoints/destinations/uuid.yaml

spec/endpoints/replies/accept/uuid.yaml

spec/endpoints/replies/attachments/uuid.yaml

spec/endpoints/replies/index.yaml

spec/endpoints/replies/reject/uuid.yaml

spec/endpoints/replies/uuid.yaml

spec/endpoints/submissions/index.yaml