Update to Substrate master (#176)

* 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
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