* Make mempool aware of MaxGas requirement
* update spec
* Add tests
* Switch GasWanted from kv store to persistent kv store
* Fix typo in test name
* switch back to using kvstore, not persistent kv store
* remove gogoproto from tools
because it's not a binary
* update protobuf version to 3.6.1 in `make get_protoc`
* update libs/common/types.pb.go and rpc/grpc/types.pb.go
* fix app tests