go/tendermint: Figure out if we can disable fixed interval empty block generation

Right now tendermint is generating tendermint blocks at a fixed interval, regardless of if there are any ABCI calls or not (empty blocks will be generated periodically). This is rather inefficient and results in significant tendermint state growth.

We should figure out what alterations to tendermint are required to have variable interval/conditional empty block generation, if such a thing is possible.

Note: The current roothash timeout implementation leverages tendermint's periodic block generation to drive timeouts. While we are at the "semi-trust the leader" stage, we may be able to have the leader drive timeouts with an explicit transaction, and disable empty block generation.