WIP: layout ideas, 2nd

- Make domains top-level, with /v1 and /sys below. Rationale: Domains will
  want to version their APIs independently. Domains are unlikely to go away,
  so having them at the top-level does not really introduce any restrictions.
  Having a private `/{domain}/sys` in parallel with `/{domian}/v1/` (public
  API) is shorter and lets us version the internal interface independently
  (using sys2 for example).

- Sketch a global config. Make it domain-oriented, so that we can build up
  routing around that. Can use yaml features to reuse / share repetitive
  elements, or build up the per-domain config from feature-oriented configs
  like InitializeSettings.php in production.