Run checks against protocol schemas

[jonnor]

There now exists some JSON schemas which formally describes the protocol, at https://github.com/flowbased/fbp-protocol

We should make it hard to do things which are incompatible/wrong according to the protocol, so we should check both sent and received messages against the JSON schemas.

Initially there are likely incompatiblities between existing implementations and current schemas, either due to bugs in runtime/client following protocol spec, or due to bugs in the schemas. So probably the checks should not fail, but instead raise a warning.

Since the BaseRuntime is an EventEmitter already, I propose we emit a validation-error event. And that we log these warnings, so people are more likely to discover and fix them.

For forward compatibility, unknown messages (not existing in schema) should be ignored. We could emit a unknown-message, and allow to opt-in to log these.

[bergie]

We're now doing this in the higher-level fbp-client library:

https://github.com/flowbased/fbp-client