Cis4

[abizjak]

Purpose

Client for interacting CIS4 registry contract.

Changes

• Add a CIS4 client to interact with a CIS4 credential registry contract.
• Add a web3id module to retrieve data from a CIS4 contract in order to validate web3id credentials.

Checklist

• [x] My code follows the style of this project.
• [x] The code compiles without warnings.
• [x] I have performed a self-review of the changes.
• [x] I have documented my code, in particular the intent of the hard-to-understand areas.
• [x] (If necessary) I have updated the CHANGELOG.