Check for jobs in 'cancel-requested' or 'requeued' statuses, and ensure
they transition to the right status. This happens at startup, before
even starting the web interface, so that a consistent state is presented.
When the job status changes, it impacts the task statuses as well. These
status changes are now no longer done with a single database query, but
instead each affected task is fetched, changed, and saved. This unifies
the regular & mass updates to the tasks, and causes the resulting task
changes to be broadcast to SocketIO clients.
Manager now sends out task updates via SocketIO, and the web interface
handles those.
Note that there is a `BroadcastTaskUpdate()` function, but not a
`BroadcastNewTask`. The 'new job' broadcast is sent after the job's
tasks have been created, and thus there is no need for a separate
broadcast per task.
Direct copy of the Flamenco Server Python code, for handling the change
of a job's status to trigger status changes on its tasks.
Not yet connected to the rest of the Manager logic.
The task status change → job status change code is a direct port of the
Flamenco Server v2 code written in Python.
There is no job status change → task status changes logic yet, and the
tests are also far from complete.
