Make signed source package for PPA
Squashed 'core/' changes from c078fe4..01c9445

01c9445 Make debuild-signed.sh reusable

git-subtree-dir: core
git-subtree-split: 01c944556d450608f02aeb705e86b448182f7807
Merge commit 'c119d2ccb8b2286604338eb245c5feabaa31bb82' into feature/plugindeb