title: Add/modify a Corpus resource

User->Datum.js: save()
Datum.js->Corpus.js: set(json)
Corpus.js->CouchDB: POST/PUT json
note right of CouchDB: CouchDB _security verifies user has access,\n  && _design/blockNonContribAdminWrites\n verifies write permissions
CouchDB-->Corpus.js: rev
Corpus.js-->Datum.js: rev
Datum.js-->User: render()
