Add the genesis hash to Transaction<T>

[dahlia]

In order to prevent inapplicable transactions (made for a different network) polluting the network, I suggest to add Transaction<T>.GenesisHash property.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. Thank you for your contributions.

[dahlia]

(See also the discussion from the Discord in Korean.)

There is a corner case where transactions belonging to a genesis block cannot determine its belonging genesis block hash. Two ways to solve this:

1. Transaction<T>.GenesisHash be optional (i.e., HashDigest<SHA256>? instead of HashDigest<SHA256>), and if and only if a transaction belongs to a genesis block the field can be null.
2. Disallow genesis blocks to have any transactions.

Personally I prefer the first way. Any ideas? /cc @planetarium/libplanet @limebell

[limebell]

Since genesis block may contain initial data, first way looks better to me too. I'll try to work on this issue based on this idea.