Make UpdateConsensus to choose the proposer

Foundry host eventually has to use the 0th validator given by `UpdateConsensus`, as the proposer.
This will remove old CodeChain proposer selection logic https://github.com/CodeChain-io/foundry/pull/602#pullrequestreview-556853470.
And also, to express complicated staking rule considering tendermint process, we have to pass the current view (round) to the module, via `block_opened()`.