Transfer assets to alphabet nodes at neofs.Withdraw

[alexvanin]

To withdraw assets, alphabet nodes should accept it by invoking neofs.Cheque method in main net. This costs real GAS and should be payed by someone. We can take fee from the withdraw invoker.

To do:

• find out max cost of cheque operation (see Do not store used cheques in neofs.Cheque method #69 to reduce cost),
• transfer this cost to each alphabet node at neofs.Withdaw.

[alexvanin]

We can do that differently when main chain will support notary contract. Then NeoFS contract can be used as a GAS payer and fee will be pretty much constant.