Master backports (#571)

* Update to latest Substrate master (#570)

* Bump substrate/version (#557)

* Bump version and Substrate (#560)

* Bump version and Substrate

* Bump version and Substrate

* Bump versions

* bump substrate to release specific v0.6.15

* Update lock

* Prepare Polkadot update for Substrate runtime interface 2.0 (#563)

* Prepare Polkadot update for Substrate runtime interface 2.0

* bump substrate to release specific v0.6.15

* Switch to `polkadot-master`

* Version bump

* Master backports

* Bump runtime

* Fix tests

* Fix tests

* Another fix.