CD: Add gitlabci

Signed-off-by: Chris Fiege <chris@tinyhost.de>

.gitlab-ci.yml

+deployment:
+    stage: deploy
+    only:
+    - /^testbed*$/i
+    - /^master*$/i
+    script:
+    - echo $CI_COMMIT_REF_SLUG > REF_SLUG
+    - make html
+    - touch /var/www/hackenopenair.de/$CI_COMMIT_REF_SLUG/htdocs/foo
+    - rm -r /var/www/hackenopenair.de/$CI_COMMIT_REF_SLUG/htdocs/*
+    - cp -r output/* /var/www/hackenopenair.de/$CI_COMMIT_REF_SLUG/htdocs/
+    - chmod go+r -R /var/www/hackenopenair.de/$CI_COMMIT_REF_SLUG/htdocs/*