[state] expose ChainID and Params

```
jaekwon
Yeah we should definitely expose ChainID.
ConsensusParams is small enough, we can just write it.
```
https://github.com/tendermint/tendermint/pull/676#discussion_r144123203

node/node.go

@@ -145,9 +145,6 @@ func NewNode(config *cfg.Config,
 			return nil, err
 		}
 		state.Save()
-	} else {
-		state.SetChainID(genDoc.ChainID)
-		state.SetParams(genDoc.ConsensusParams)
 	}
 	state.SetLogger(stateLogger)
 
@@ -163,8 +160,6 @@ func NewNode(config *cfg.Config,
 
 	// reload the state (it may have been updated by the handshake)
 	state = sm.LoadState(stateDB)
-	state.SetChainID(genDoc.ChainID)
-	state.SetParams(genDoc.ConsensusParams)
 	state.SetLogger(stateLogger)
 
 	// Transaction indexing