Implement a framework for interacting with known contracts (Dapps)

[zah]

This is item 17 from the Nimbus roadmap.

We need to implement a Nim framework similar to web3.js and web3.py that is able to talk to any of the existing Ethereum clients over their JSON-RPC interface. Such a framework is able to describe a contract through their public interface, to execute transactions given well-typed parameters and to monitor the announced new blocks for log events produced by the contract.

Out initial target will be to monitor the upcoming Validator deposits contract, whose log events will be consumed by our beacon chain implementation.

Sub-tasks:

• Nim-types-to-ABI-types translation and contract FFI DSL.
• Transaction creation logic
• Event monitoring logic
• Provide high-level information about the contract for the UI layer (NatSpec, etc)

[zah]

This has been implemented as https://github.com/status-im/nim-web3