Use and pin protoc-gen-go 1.0.0

This modifies our build script to pin the exact protoc-gen-go version we use. In the process, it re-generates the go wrappers with protoc-gen-go 1.0.0.

Before this change we were using the master branch of the github.com/golang/protobuf repo.

Sorry about the confusing branch name, this MR started out using protoc-gen-go 1.1.0 but that caused too much churn so I targeted 1.0.0 instead.

In passing, I am also updating the Go version used by CI to Go 1.10. This makes life easier for contributors who are running Go 1.10 (and harder for all other Go versions...).