Hotstuff 2

[bfish713]

Closes #<ISSUE_NUMBER>

This PR:

This PR introduces the Hotstuff 2 consensus rules. Hotstuff 2 is has some notable changes over the original. These are:

• The decide rule goes from a 3 chain to a 2 chain
• The leader must wait for a QC from the last view (like before) or for a set timeout to collect the highest QC from all other replicas. The leader proposes with the highest QC it's received
• Nodes send the highest QC they've seen to the next leader when a view finishes.
• The locked QC becomes the what was before the "high qc"
  • In other words replicas will not vote for any proposal with a justify QC from a lesser view than any justify QC they previously saw.

This PR does not:

Key places to review:

[lukaszrzasik]

I'd just like to clarify two things before merging. Other than these two doubts I think it's good to go.