Add a small wrapper around github.com/google/uuid. That way it's clearer
which functionality is used by Flamenco, doesn't link most of the code to
any specific UUID library, and allows a bit of customisation.
The only customisation now is that Flamenco is a bit stricter in the
formats it accepts; only the `xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx` is
accepted. This makes things a little bit stricter, with the advantage
that we don't need to do any normalisation of received UUID strings.
Add `fetchJobTasks` operation to the Jobs API. This returns a summary of
each of the job's tasks, suitable for display in a task list view.
The actually used fields may need tweaking once we actually have a task
list view, but at least the functionality is there.