Add support structure for Go code parts

The Go code parts (gateway, ducc, snapshotter) should get a (common) support structure:

• Agree on a coding convention (gofmt, golint)
• Add a linter to the CI
• Add unit test runs to the CI
• Binaries should report the version number and help text on v, version, h, help command line flags; the version should be bumped up on with the bump_version.sh script