v0.17.7

1. Add the finalized block concept. Finalized blocks cannot be reorged, which protects the network against deep reorgs.
2. Add the -maxreorgdepth configuration to configure at what depth block are considered final. Default is 10.

1.增加不可逆配置，防止51%攻击。
2. maxreorgdepth 默认 10。