Bring recent metno/python3 updates inline with requirements at smhi

[adybbroe]

This PR does a few things:

• Cleaning up after recent merged PRs from Met Norway
• Add trollsift to required packages and fix utils
• Update versioning - use setuptools_scm to handle versioning
• Add pygrib as a requirement
• Add hook to let PPS send posttroll messages

[TAlonglong]

At least you need to change here https://github.com/pytroll/pytroll-pps-runner/blob/master/nwcsafpps_runner/metno_update_nwp.py#L31

change helper_functions to utils and remove run_shell_command

[adybbroe]

@TAlonglong I am merging this now. I hope you will be able to handle it!?

[pnuu]

The PR just came "ready for review" 8 minutes ago. Please give some time for the review.

[adybbroe]

Yes, right @pnuu ! I will try hard waiting till after Easter in case @TAlonglong is not online these days