Withdraw operation works a bit different with neo:morph.
User calls "Deposit" and "Withdraw" methods that produce
notifications for the inner ring nodes.
"Deposit" method does not produce feedback, but "Withdraw"
does. Inner ring nodes check if user eligible to withdraw
assets. If so, nodes invoke "Cheque" method. This method
collects invocations from inner ring nods. When there are
2/3n + 1 invocations, smart-contract transfers assets back
to the user and produces notifications.
Inner ring nodes do not collect signatures for the cheque now.
Instead they invoke "InnerRingUpdate" method and smart-contract
checks if method was called from inner ring node. Then it
accepts cheque if there were 2/3n+1 invokes.
With neo:morph environment, there will be no direct communication
between inner ring nodes and storage nodes. neo:morph smart-contracts
will identify inner ring nodes by their signatures.
Inner ring nodes check their presence in inner ring list during
startup. "IsInnerRing" method allows to check presence efficiently
by calling this method.
