zero balance account creations

[barryWhiteHat]

We want to make it cheaper to make zero balance accounts. So we add an extra smart contract call zero_bal_account_creation which only the operator can call.

1. This provies a merkle root as a public input to a snark
2. The snark proves that the balance is zero for every leaf in the merkle tree.
3. The smart contract then appends this to the deposit que as defined Deposit coins to smart contract into snark side chain #2