Review Board 5.0

This will be a small release focused on a couple features that outgrew Review Board 4.0, and a move to a modern Django and Python.

It is targeted for early 2022.

• Update to Django 3.2 LTS, and Djblets 3.0 (@see Djblets Roadmap)
• Drop Python 2.7 and 3.6.
• New Features:
  • Code safety checks
  • Elasticsearch 5.x and 7.x
  • Initial DiffX support
  • New diff file ACL capabilities
  • New diff metadata storage

Review Board 6.0

<aside> ⚠️ This is not a complete list of planned features.

It's just a series of notes on concrete work we're expecting, for coordination with some third-parties we're working with, mostly focused on architectural changes.

</aside>

• Update to Django 3.2 (or newer) LTS, and Djblets 4.0 (see Djblets Roadmap)
• New Features:
  • Accessibility options for Image Review
  • Standardized keyboard shortcuts and help UI
  • Registry-backed SCMTools