There's still plenty of dependencies on account/device DBs, but this
is a start. This is a breaking change as it adds a required config
value `listen.user_api`.
* Split out adding HTTP routes from making internal APIs for clarity
* Split out more components
* Split out more things
* Finish converting
* internal mux for internal routes
* Separate muxes for public and internal APIs
* Update client-api-proxy and federation-api-proxy so they don't add /api to the path
* Tidy up
* Consistent HTTP setup
* Set up prefixes properly
