This PR changes ABCI time format from int64 (Unix seconds) to WKT (WellKnownType) google.protobuf.Timestamp.
Refs #1857
Reasons:
better precision
standard DT for proto
* update Gopkg.lock
* [makefile] remove extra grep
- go list excludes vendor by default now
* proto3 timestamp
* [docs/abci-spec] note about serialisation format
* make time non-nullable
Refs #1861
We don't use the fee field and its likely just confusing.
We can add backwards compatible priority (instead of fee) later.
Note priority is better than fee because it lets the app do the math on how to rank order transactions, rather than forcing that into tendermint (ie. if we return fee, priority would be fee/gas)
Anton Kaliaev
Peng Zhong
Zach Ramsay