Revert changes to the BlockID and PartSetHeader

[evan-forbes]

Summary

In order to pull changes from upstream and treat tendermint more as a "black box", we should revert the changes that we have been making to the BlockID and the PartSetHeader.

Details

As described in ADR 007 #504, we will be treating our fork of tendermint more like a black box in that we make as few changes as possible. This means that we will revert our efforts to remove the PartSetHeader.

Action Items

• revert Remove the PartSetHeader from VoteSetMaj23, VoteSetBits, and state.State #479
• revert Stop Signing over the PartSetHeader for Votes and remove it from the Header #457
• revert Decouple PartSetHeader from BlockID #441

References

tracking #491
blocking #506