[PBFT] TODOs (moved from initial merge request)

[zzlyn]

To be done:

• doing message "digest" and server authenticity checks and providing capability to detect "arbitrary" messages or "hijacked" servers (Abhi, Walter)
• finishing PBFT view change logic (Robert)
• adding a client node, and implementing the proper logic for trying the primary first, then multicasting if a timeout is reached, and the 2f+1 replies to the client (details of this are in the paper in section 4.1) (Robert to open issue, Daniel to look into)
• verify and implement pre-prepare stage (Walter)
• verify and implement prepare stage (Abhishek)
• verify and implement commit stage (Daniel)
• update the log to order requests by the pre-prepares received, not the order of writing to the log
• show committed vs written (i.e. pre-prepare received) in the log

Lower priority:

• adding PBFT checkpoint logic

[zzlyn]

Original Issue: zzlyn/ConsensusVisualization#79