worker shutdown handling

[scones]

updated for wrong assumption

feature

please make the signal handling configurable per signal.
i'd like the handling of shutdown on SIGINT and SIGTERM, instead of a hard exit to make sure no data is lost.
Since i plan to scale my workers through docker scaling, the workers within the containers will receive a SIGTERM on downscaling, on which i'd like to wait for the job to finish before closing the worker.

[merlindorin]

Seems a lot of work, if you want to make a PR, I will appreciate to make a review :D ;)