Derive Block from Hare Output Set

[noamnelke]

When the Hare completes we'll now want to generate a Block and store it in a separate database.

We'll use the same mechanism we use today to create a list of ordered transactions (mesh.extractUniqueOrderedTransactions()), to generate a Block. In addition to an ordered list of transactions, a block should contain a list of rewards. This should be derived from the list of smeshers that authored the proposals that the Hare agreed on. For each smesher we'll find the coinbase address in the relevant ATX and add a reward proportional to the number of proposals/ballots authored by them and included in the Hare output set.

Blocks should be persisted to a BlockDB. When the node calculates a block from Hare results, it should also store a value in a layer -> block index in the same database. To be explicit - we should NOT store a value in this index if we add a block to the database because we've synced it or fetched it from a peer, only when we've created it ourselves based on Hare results.