baseapp: NewBaseApp takes a Codec

[ebuchman]

This is awkward in the documentation since we have to pass in a codec but then might overwrite it with SetTxDecoder. I think we should either pass in a TxDecoder and remove SetTxDecode, or not pass in anything and just use SetTxDecoder (and maybe expose a AminoTxDecoder(cdc *wire.Codec) TxDecoder

[rigelrozanski]

+1 for removing SetTxDecoder, when would we ever even want to modify the decoder after we've created the baseapp anyways?

[alexanderbez]

Seems that cdc codec is used in BaseApp#Query. Apart from that, it makes sense to have the constructor take a TxDecoder 👍