New purchase logic proposal

[ZenVoich]

Diagram:

Pseudo code:

public func receive(caller : Principal, tokenId : Types.TokenIdentifier) : async Result.Result<(), Types.CommonError> {
  // if token is not available refund ICP
  if (not tokenAvailable(tokenId)) {
    addRefund(caller, tokenId);
    return #err;
  };

  let paid = await checkPayment(caller, tokenId);
  if (not paid) {
    return #err;
  };

  if (not tokenAvailable(tokenId)) {
    addRefund(caller, tokenId);
    return #err;
  };

  transferToken(caller, tokenId);
  addDisbursement(fees);
  addDisbursement(tokenOwner);
  return #ok;
};

accountId for payment computed from canisterPrincipal + userPrincipal + tokenId
In addRefund we add cron job to return icp to user if payment was recieved and token was sold to another user.
In addRefund we also check if there any deferred disbursements in conflict with refund. (if the same user is calls receive multiple times)

Pros:

1. Fewer steps to buy NFT
2. No lock logic. No one can lock entire collection
3. ???

Cons:

1. Backwards incompatible. Other marketplaces should implement the new logic.
2. Sometimes(rarely?) we need to refund ICP(fee but low)
3. ???