Now that the images are built in a schedule.

- pre-commit.
- Address a few issued from pre-commit.
- GitLab CI.
- License.
- Stricter .dockerignore.
- Add contact info to README.
- Personal registry.

The builds have been broken for a while. Because the knot image is based
on Debian. Use Alpine instead (not because I'm sure the image will be
smaller or better, but it's less work to keep the existing Alpine
stuff).
Also, run as a limited user.

# Conflicts:
#	Dockerfile

- Use Knot resolver instead of Unbound (results in smaller image but nothing more, updated to Stretch).