Implementation spec of Double Signing Risk Reduction [ADR-51](https://github.com/tendermint/tendermint/blob/master/docs/architecture/adr-051-double-signing-risk-reduction.md) by B-Harvest - Add `DoubleSignCheckHeight` config variable to ConsensusConfig for "How many blocks looks back to check existence of the node's consensus votes when before joining consensus" - Add `consensus.double_sign_check_height` to `config.toml` and `tendermint node` as flag for set `DoubleSignCheckHeight` - Set default `consensus.double_sign_check_height` to `0` ( it could be adjustable in this PR, disable when 0 ) Refs - [ADR-51](https://github.com/tendermint/tendermint/blob/master/docs/architecture/adr-051-double-signing-risk-reduction.md) - [https://github.com/tendermint/tendermint/issues/4059](https://github.com/tendermint/tendermint/issues/4059) - [https://github.com/tendermint/tendermint/pull/4262](https://github.com/tendermint/tendermint/pull/4262)