Add "ConsensusParams" to baseapp

[cwgoes]

Ref #963 (comment)

Also ensure MaxGasPerTx is enforced by baseapp.

[mossid]

Does ConsensusParamUpdates in abci.ResponseEndBlock overrides the existing ConsensusParams only for the non-nil values of the ConsensusParamsUpdates or overrides all? @ebuchman

[ebuchman]

It only over-rides the non-nil fields in ConsensusParamUpdates. See https://github.com/tendermint/tendermint/blob/v0.25.0/types/params.go#L104.

This means if it wants to eg update the BlockSize.MaxGas, it has to fill out the full BlockSize, so the MaxBytes and the MaxGas. Should we consider changing this behaviour? In any case I don't think this is properly documented Tendermint side!

[jackzampolin]

Should this be in the paramStore instead? Or is baseApp the right way to go here?

[alexanderbez]

We have params both in the base app and the context