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
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