Persist configuration through Redis on changes

* Don't put Redis into SUB mode after fetching initial config. Removes unused
  ability for external configuration updates, but allows us to use that client
  to save our own updates from the admin API / UI.
* Save all configuration to Redis, not just streams
* Streams: add config() method to return our configuration
* API: Add POST /streams endpoint for adding a stream
* Update slave and proxies to use the new config format