Moving UntypedBlock and UntypedTransaction from Libplanet.Node to Libplanet main project

[tkiapril]

As I've been working with indexing, I often found it inefficient to deal with Block<T> and Transaction<T>, as they need to be instantiated with IAction types, and as of now they are cryptographically verified during instantiation. This causes a lot of overhead when we have to deal with a large number of these instances even where a full instantiation is not required (when evaluation is not required.) Recently ITransaction is added, and using Transaction<T> as ITransaction makes it a bit more efficient when dealing with these stuff. However, there is still no way of instantiating an unverified ITransaction instance, nor there is a concrete subtype of ITransaction. Thus, I suggest that we bring UntypedBlock/UntypedTransaction to Libplanet main project and create IStore methods to retrieve unverified blocks/txs.

[tkiapril]

On the daily meeting, we came out with an idea to first make an unverified block/tx concrete type under the Libplanet.Store namespace, and create API to retrieve unverified instances from IStore. These concrete types should be made so that they are not misused instead of current Block<T> and Transaction<T> types. When we start isolating ActionEvaluator<T> outside of BlockChain<T>, we can think of how to deal with these concrete types, whether to take them out of Libplanet.Store namespace; An idea is that we can have both UnverifiedTransaction(tentative naming) and Transaction(without a <T>) inherit ITransaction and have a similar layout, but have them as a different types so that they cannot be cast to each other. Then, we can have an UnverifiedTransaction.Promote() method that verifies the transaction and returns a Transaction instance.