Currently a collator will only send a collation to validators it is a
primary for. While testing this could lead to the situation that the
same collator was registered as prime for all Parachain validators but
failed for other reasons to generate a PoVBlock. However no other
collator was sending a collation, which stopped the Parachain until the
faulty collator was stopped.

This pr solves this problem by making sure that every collator sends a
collation to one of his validators he is connected to, but registered as backup.

* extract all network code to legacy submodule

* update references to legacy proto

* skeleton of futures-based protocol

* refactor skeleton to use background task

* rename communication_for to build_table_router

* implement internal message types for validation network

* basic ParachainNetwork and TableRouter implementations

* add some module docs

* remove exit-future from validation

* hack: adapt legacy protocol to lack of exit-future

* generalize RegisteredMessageValidator somewhat

* instantiate and teardown table routers

* clean up RouterInner drop logic

* implement most of the statement import loop

* implement statement loop in async/await

* remove unneeded TODO

* most of the collation skeleton

* send session keys and validator roles

* also send role after status

* use config in startup

* point TODO to issue

* fix test compilation

* Bump versions

* Update for tipping treasury

* Bump substrate

* Fixes

* Put send_consensus back in.

* Fix test

* Fixes

* Fixes

* Fix warning

* rename crates as appropriate

* Rename to use master - easy to revert, but shows it's working

* Bump runtime version

* Bump version

* Bump Substrate again

* Integrate srml/im-online

* Fix all build errors with old aura.

* Fix most of the build errors.

* Builds and tests seem to pass (I will not trust this commit yet)

* Apply suggestions from code review

Co-Authored-By: Robert Habermeier <rphmeier@gmail.com>

* Kill some warnings.

* fix panics on 0 validators

* Fix dev chain.

* Fix author stuff

* fix im online integration.

* Some tweaks

* Introduce app-crypto

* Initial build work

* codec update / tweaks

* patch polkadot-erasure-coding input

* More fixes for new crypto

* More fixes

* Update parachains module

* evamp parachain crypto

* More crypto work.

* Chain spec and service.

* ChainSpec stuff

* Last bits for a clean build

* Tweak coment

* adapt polkadot-validation to the new keystore

* polkadot-network compiles, but tests don't

* Integrate the new parachain validation stuff

* delete message_routing file

* make polkadot-network tests compile and pass

* runtime tests compile and pass

* update substrate ref

* service compiles

* all tests pass

* Add TODO, change branch back to polkadot-master

* Lock file

* TODOs done

* Issue number

* Remove old tODO

* Remove commented code

* Update to master

This introduces a new type `CollatorId`, currently just `SessionKey`
but which would forseeably change to its own thing. It seems to work
like this (despite there being a lot of the new-incompatible
`AccountId` replaced). No idea if it does anything sensible, though.

* Cleanups

* Fix tests

* Remove commented code

* Specify commit hash

* Remove commented code

* Correct version

* Update runtime/Cargo.toml

Co-Authored-By: gavofyork <github@gavwood.com>

* PairT instead of _Pair

* Update lock file

* Remove rev causing upset

* skeleton of collators object

* awaiting and handling collations. rename `collators` to CollationPool

* add some tests

* add tests

* implement Collators trait for ConsensusNetwork

* plug collators into main polkadot-network

* ignore collator role message

* add a couple more tests

* garbage collection for collations

* extract session-key tracking from consensus

* add local_collations.rs

* finish polish of local_collations

* integrate local_collations into network layer

* introduce API for adding local collations

* mostly finish collator implementation pending service fix

* Specialized network()

* push collations to the network

* grumbles

* substrate-service has custom configuration

* initialize network in collator mode as necessary