Allow E2E testing with live-chain state

[cmichi]

We got it working by now and @brunopgalvao wrote the instructions down here: use-ink/ink-docs#283.

For this to work though, my custom ink branch https://github.com/paritytech/ink/commits/cmichi-use-sc-chopstick-compatible-2 has to be used. It contains only two commits though.

Please create a PR against master that implements those two changes properly. My branch is hacky and contains some unnecessary changes (you'll see them).

• Allow specifying the WS_PORT of the RPC node.
• Add a feature unstable-light-client to ink!. If passed on the command-line the effect should be this.

Please test if the instructions from Bruno's PR still work with your PR.