Replace the writeonly blockchain storage with events

[nikeshnazareth]

[nikeshnazareth]

The AnonymousVoting contract stores IPFS hashes (for params, registration and voting) that are not referenced within the contract. Instead, the contract simply tracks their existence. It is up to the client to retrieve and validate the content. We could save storage space by putting the hashes into contract events, and only store booleans to track the registration and vote status of each participant