sc-chain-spec: getting ready for non-native world

- adds support for:
  - JSON based GenesisConfig (patch/full-config) to ChainSpec allowing
    interaction with runtime GenesisBuilder API.
  - interacting with arbitrary runtime wasm blob to chain-spec-builder command line util,
  - GenesisBuilder API in kitchensink runtime
- removes `code` from system_pallet
- adds `code` to the ChainSpec
- deprecates ChainSpec::from_genesis, but also changes the signature of
  this method extending it with code argument. ChainSpec::builder()
  should be used instead.
- implements GenesisBuilder API for node-template-runtime and kitchensink-runtime.

Squash commit of work made in: https://github.com/paritytech/substrate/pull/14562