Add basic cosmwasm support

[jstuczyn]

While using the library in conjunction with cosmwasm-based cosmos validators, I found myself writing bunch of code that I figured could instead be contributed back to the community.

This pull request introduces basic support for wasmd. It includes compilation of the protobuf files and conversion of Msg types into something that can be more easily put into Tx Body.

I realise most people would not need it, so I've left it feature-locked behind cosmwasm feature flag.

[tony-iqlusion]

Thanks! This is definitely interesting.

I'm on vacation and don't have time to review it right now, but perhaps @jkilpatr could take a look in the meantime

[zmanian]

This looks good to me.

I don't really know what the answer should be for tracking compatibility with multiple upstream versions should be.

wasmd and the cosmos SDK being versioned independently.

[tony-iqlusion]

Looks good, thanks!