This commit adds a breached contract retribution storage layer using
boltdb to the breach arbiter. The breach arbiter now stores retribution
state on disk between detecting a contract breach, broadcasting a
justice transaction that sweeps the channel, and finally witnessing the
justice transaction confirm on the blockchain. It is critical that such
state is persisted on disk, so that if our node restarts at any point
during the retribution procedure, we can recover and continue from the
persisted state.
