consensus: partial consensus message decoding

[AnnaShaleva]

closes #849

[AnnaShaleva]

Also checked on privnet

[codecov]

Codecov Report

Merging #862 into master-2.x will decrease coverage by 0.00%.
The diff coverage is 76.19%.

@@              Coverage Diff               @@
##           master-2.x     #862      +/-   ##
==============================================
- Coverage       67.86%   67.86%   -0.01%     
==============================================
  Files             142      142              
  Lines           13422    13433      +11     
==============================================
+ Hits             9109     9116       +7     
- Misses           3897     3900       +3     
- Partials          416      417       +1     

Impacted Files	Coverage Δ
pkg/consensus/consensus.go	40.44% <16.66%> (-0.62%)	⬇️
pkg/consensus/payload.go	97.43% <100.00%> (+0.12%)	⬆️
pkg/consensus/recovery_message.go	84.33% <100.00%> (ø)

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[roman-khimov]

closes #859

Really?