Make `nil` as a default value for attributes.
Document field values of instance constructed
via `New`. Assert the values in corresponding
unit test.
Signed-off-by: Pavel Karpy <carpawell@nspcc.ru>
Replace owner.NEO3Wallet usage with owner.ID usage. Functions that process
the wallet address convert it to the owner identifier through the public
method.
Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>
