Create a `RawGenesisBlockBuilder`

[appetrosyan]

Motivation

For testing it's better to set up assets/accounts/domains in the genesis block. We currently don't have a convenient interface to do that.

example

RawGenesisBlockBuilder::new()
    .with(Domain("wonderland"))
    .with(Account("alice@wonderland"))
    .with(Asset::BigQuantity("roses")
            .initially(100)
            .owned_by("alice@wonderland"))
    .finish()