Write proposal for interacting with Tendermint Core Validator set

[martyall]

There are a few abci messages that deal with the validator sets in tendermint core, updating that voting rights, and potentially slashing. To be clear, we'd probably have to learn more about tendermint before we can even articulate what we want to do.

There are a few suggestive cosmos-sdk modules where these things get picked up:

1. https://github.com/cosmos/cosmos-sdk/tree/master/x/slashing
2. https://github.com/cosmos/cosmos-sdk/tree/master/x/staking
3. https://github.com/cosmos/cosmos-sdk/tree/master/x/evidence

Some of this stuff is probably cosmos specific, which we don't necessarily care about right now. The point here is to figure out something like:

Given that tendermint is a proof of stake consensus algorithm, and the stake balances and denominations are being held buy the abci application, how does the abci application need to react to messages that contain updates about this information from tendermint core?