feat(spec): Improvements and fixes in consensus overview (#738)

* spec/consensus: improvements in Tendermint overview

* spec/consensus: improvements in Tendermint overview

* spec/consensus: precommit step reviewed

* spec/consensus: added exit conditions section

* spec/consensus: exit conditions section updated

* spec/consensus: messages section updated

* spec/consensus: proposals section reviewed

* spec/consensus: proposals section and equivocation

* spec/consensus: votes section reviewed

* spec/consensus: votes section and equivocation

* Apply suggestions from @josef-widder

Co-authored-by: Josef Widder <44643235+josef-widder@users.noreply.github.com>
Signed-off-by: Daniel <d.cason@gmail.com>

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Signed-off-by: Daniel <d.cason@gmail.com>
Co-authored-by: Josef Widder <44643235+josef-widder@users.noreply.github.com>