GitLab

ci: adjust schedules

See merge request !905

With Gitlab 10.7 variable support in pipeline only/except, it's now
possible to execute OBS builds with a nightly schedule, while keeping
the docker image builds on a weekly schedule.

https://docs.gitlab.com/ee/ci/variables/#variables-expressions

docker: use sensible defaults

Closes #583

See merge request !903

knot: add support for ECS EDNS option

See merge request !904

Log dnssec no diff

See merge request !901

This reverts commit 4fbcaf75.

fixes #581

Use default configuration file with example zone file and drop the
user to interactive knotc cli when launched.

Fixes #583

doc: roughly described zone load process

See merge request !900

close #582

zone load: if computed diff and soa unchanged, increment it

Closes #234

See merge request !899

Relates to #572