Call for papers peer review workflow

This is a continuation of #204 (closed). The call for papers review workflow is currently optimised for the Budapest conference.

After allowing all event types for review, we found the following:

1. One can create only one Special Session.
2. One can create as many poster and participatory sessions as wanted.
3. After creating an individual paper, all submissions will be closed, but review allowed

This is encoded in https://lab.allmende.io/degrowth/scriptorium/blob/deployment/app/models/ability.rb

@gandhiano suggests to work with @mladen and @viktoriya.kulikova around the past and current requirements and redesign the flow as intended.