Builder pattern for creating boxes

[greenhat]

Like the following:

 let math_bounty_candidate = create_candidate(
            bounty_amount_in_nano_ergs,
            &"94hWSMqgxHtRNEWoKrJFGVNQEYX34zfX68FNxWr".to_string(),
            &vec![],
            &vec![],
            current_height,
        )

would become something like

let math_bounty_candidate = CandidateBuilder::new(bounty_amount_in_nano_ergs, &"address".to_string(), current_height)
.build();

and if you add tokens :

let math_bounty_candidate = CandidateBuilder::new(bounty_amount_in_nano_ergs, &"address".to_string(), current_height)
.set_tokens(tokens)
.build();

Or even breaking new into separate methods to "name" parameters:

let math_bounty_candidate = CandidateBuilder::with_value(bounty_amount_in_nano_ergs)
.with_address(&"address".to_string())
.with_height(current_height)
.with_tokens(tokens)
.build();