Support a standard consensus like PBFT

[prem-baranwal]

Support a full-fledged rust based consensus as default consensus. Choices could be a) Proof of Authority with more than one validator) or b) PBFT or c) Go-Sig
We need not implement it from scratch.

[diyism]

It seems that gosig is very promising, wish that simpleblockchain could support the gosig protocol.
Ref:
https://www.cs.toronto.edu/~fanl/papers/gosig-socc20.pdf
https://github.com/gauravagarwaltal/consensus_gosig

Besides, I think that a database with consensus/consortium/covenant is far more simpler to use than a blockchain,
for example BFTDB, but it used tendermint, it's not as scalable as Gosig protocol:
davebryson/bftdb#3