Collators get incoming parachain messages (#149)

* refactor out a consensus data fetcher from table router

* move statement checking logic into router

* refuse to start authority if collator

* support building the table router asynchronously

* instantiate_consensus does not overwrite old

* update key in new consensus if there was none before

* collator collects ingress from network

* test produced egress roots

* fix adder-collator compilation

* address first grumbles

* integrate new gossip with collator network launch

* address review

polkadot/service/src/lib.rs

@@ -212,6 +212,13 @@ construct_service_factory! {
 					None => return Ok(service),
 				};
 
+				if service.config.custom.collating_for.is_some() {
+					info!("The node cannot start as an authority because it is also configured\
+						to run as a collator.");
+
+					return Ok(service);
+				}
+
 				let client = service.client();
 				let known_oracle = client.clone();