Create PouchDB design document on startup

[petteripitkanen]

Currently the PouchDB design document with the validate_doc_update function is created during npm run migrate with an HTTP call. It would be more robust to also check that the design document exists and is up-to-date on startup, and since it is a normal document to create it with the PouchDB methods instead of HTTP. See pouchdb-design.

[petteripitkanen]

Also, currently the design document is replicated to clients, this should be prevented probably.