Proof of concept: Add a new runtime that uses pallet_contracts (#186)

* seal: Copy over a legacy version of pallet_contracts from substrate

* seal: Fix substrate dependency pathes and add as dependency to runtime

* seal: Adapt pallet to current substrate version

* seal: Add contracts pallet to runtime

* seal: Implement rpc runtime api

* seal: Update to latest rpc output format

* seal: Replace child trie by prefix trie

* seal: Add contracts endpoint to the client

* seal: fixup rpc test

* Fix whitespace issue

Co-authored-by: Sergei Shulepov <sergei@parity.io>

* seal: Move pallet out of the runtime directory

* seal: Create a seperate runtime for contracts

* Move parachains to top level directory

* seal: Disable rent for easier testing

Co-authored-by: Sergei Shulepov <sergei@parity.io>