Fixes #697 Switched to golangci-lint, fixes issues with buildkite and does some linting fixes to appease the new linters.
Fix Docker files which had been forgotten in #594 and update scripts and docs to remove references to gb. I also removed the `jenkins` directory which is outdated. We can revert f8d7e99 if we realise that it was a mistake to do so.
f8d7e99