Finn authored Oct 06, 2020 and Finn committed Dec 06, 2020

* this change is fully backwards compatible with the v0 protocol, v1 requests must specify "version": "v1"
* v1 requests handling includes basic input validation before anything is run.
* protocol is self-documenting. signald can introspect itself and return a JSON Schema document of all request types and their responses.
* all requests types now live in their own class, which should improve code readibility