cumulus: chain-specs getting ready for non-native world

- integration-tests: storages building migrated to GenesisConfig JSON patches
- parachain-template: GenesisBuilder implemented + JSON patch in ChainSpec
- parachains/runtimes: GenesisBuilder API implemented
- chain-specs: RuntimeGenesisConfig removed, JSON patches added
- json_vs_legacy_tests: tests for json-based ChainSpecs added
    Copy of current chain_spec files (using deprecated from_genesis) was
    created in order to test json-patching vs old from_genesis version.
- chain-specs: code moved from pallet_system to ChainSpec