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I also removed the `jenkins` directory which is outdated.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.
We should no longer be building anything into vendor/bin in the scripts,
so adding it to the path can lead to all sorts of confusion if old
binaries are there.
The motivation for this is to make it easier to see whether a travis failure is due to linting, unit tests or integration test failures, without having to look in the logs.
It also means that each job is independent, so if e.g. the linting fails then the unit tests will still be run.
