Urwid is only be used for input, not display.
Now adding the minimal set of urwid modules that vigil needs.
These can be further pared down in future.
Thank you to Ian Ward.
This had stopped working.
Unfortunately it doesn't seem to help anyway.
Ideally the responsiveness of the interface is the same, regardless
of whether the workers are paused or not. Atm its much better when
they are paused.
- There is less forking, once per worker process, instead of once per job.
- Nice and ionice are applied to the worker processes and hence all jobs run
by them.
- This allows jobs to benefit from caches filled by previous jobs. For example
many tools applied to a python file need to calculate if its python2 or python3.
