Crash in all cases of undefined app behavior

[williambanfield]

During the implementation of ABCI++, it was decided that Tendermint should crash if it received an error from the application from one of the ABCI methods.

This behavior was decided as correct since an application responding with invalid data or that has become unresponsive is no longer in a consistent state. Additionally, the Tendermint algorithm can no safely longer make progress.

We should update the rest of the consensus code to crash when ABCI responds with an error or produces invalid data.