Rococo (mocky)Runtime and Client (#841)

* Implement fake rococo runtime.

* Generate correct storage key.

* cargo fmt --all

* Move client-rococo.

* Satisfy clippy.

* Apply suggestions from code review

Co-authored-by: Hernando Castano <HCastano@users.noreply.github.com>

* Address review comments.

* Clippy again.

Co-authored-by: Hernando Castano <HCastano@users.noreply.github.com>