Add prederived test accounts into options

[dudo50]

It would be nice if we can create ALICE or ALITH or other testnet accounts for user if they wish to do quick local testing, wrapping all signer logic for them into simple option in builder.

So perhaps:

Builder{
  development: true
  localhostAccount: "ALICE"
  apiOverrides { ...
  }
}

Will build and sign transaction for user.

Suggested by @franciscoaguirre . Thanks!