api: implement smart cache for new endpoints

[inyono]

• [ ] subscriptions:
  • [ ] should be set when the user changes their subscriptions.
  • [ ] should be set for new users.
• [x] revisionIds:
  • [x] should be set when a revision is created or deleted.
  • [x] should be set when a new repository is created.
• [x] restore from bin
• [x] /user/profile/:username: should be set for new users.
• [ ] events: similarly, depending on actual implementation.
• [x] /api/threads/:id and /api/uuid/:commentid (wenn commentare hinzugefügt / aktualisiert werden)

[Entkenntnis]

https://github.com/serlo/frontend/issues/645 related.