Add blacklist/whitelist type reference validation for client/server events

[etinquis]

At 'build' time, I want to determine if any client events reference types that should not be exposed to clients.

As an example, no events that get sent to the client should reference account ids, as this should be private information.

fun check(client-events, types-blacklist) {
  for(event in client-events) {
    // recursive, into refs:
    for(ref in event.references) {
      if(types-blacklist.has(ref)) {
        // fail validation
      }
    }
  }
}