Produce Epoch Block

[DanMacDonald]

Depends on #183 (at least)

There are several account balance tasks that need to happen when an epoch ends. For this to happen reliably the node that produces the epoch block must also update the account balances in the IrysVM state so that the epoch block includes these balance updates.

Other nodes which receive the epoch block must process it and apply he same account balance changes, the state_root that gets included in the Irys epoch block should also include these account balance changes.

If #183 is implemented, it is sufficient to start making tests around these epoch rewards/refund/account balance adjustments.