Add Statemint (#452)

* Add Statemint

* Versioning.

* Fixes

* Fixes

* Fixes

* Fixes

* Fixes

* Benchmarking

* kick patch (paritytech/statemin#88)

* Westmint Chain Spec (paritytech/statemint#90)

* Tidy the common .toml

* Update weights

* add westmint sudo key comment

* Port consensus stuff

* fix typo

* fix typo ... again

* Recognise Westmint

Co-authored-by: Alexander Popiak <alexander.popiak@parity.io>
Co-authored-by: Bastian Köcher <info@kchr.de>