Draft Consensus impact analysis (#552)

* Draft docs/DESIGN.md

* docs/DESIGN.md more writing; document losing scope

* docs/DESIGN.md flesh out experiments

* docs/ImpactAnalysis.md renamed from docs/DESIGN.md

* TOSQUASH reword realization to closure

* TOSQUASH quorum is the wrong word

* TOSQUASH better forward reference

Author: nfrisby