We were accepting transactions with zero system fee, but we shouldn't do
that. Also, transaction's verification execution has to be limited by network
fee.
We make it explicit in the appropriate Block/Transaction structures, not via a
singleton as C# node does. I think this approach has a bit more potential and
allows better packages reuse for different purposes.
Two changes being done here, because they require a lot of updates to
tests. Now we're back into version 0 and we only have one type of
transaction.
It also removes GetType and GetScript interops, both are obsolete in Neo 3.
Frequently one needs to check if struct serializes/deserializes
properly. This commit implements helpers for such cases including:
1. JSON
2. io.Serializable interface
