TODO

- relogon on expired creds to avoid loosing POST/PUT data

- "allow_3rd_party" for solving activities

- auth while offline posts
- do not return Context.releases while non-slave sync
- deliver spawn events only to local subscribers
- switch auth from WWW-AUTHENTICATE to mutual authentication over the HTTPS
- pull node changes periodically for checked-in contexts
- refount blobs on node and client sides to delete orphaned ones
- secure node-to-node sync
- detailed error messages for broken solves

v1.0
====
- switch to AGPL
- move API docs to sources to share them from `GET /` route
- do not subscribe on client to keep UI up-to-date

v2.0
====
- Pool topics
- (?) easy proxying from any client, e.g., from a classroom teacher
- sort out contexts by targeting auditory
  * students of ages from..to
  * educators
  * students w/ disabilities
  * etc
- sort out contexts by school subjects
- handle forks
- Post.popup_level to reproduce Q&A workflow for any topic type