Add initial .gitlab-ci.yml

GitLab provides a CI service which allows to test all commit and merge
requests automatically on arbitraty Docker images. The initial setup
includes building prerequisites which can't be provided with
'apt-get build-dep' and running
'./autogen.sh && configure && make && make check && make install'.
3 jobs for gitlab-ci in 7 minutes and 46 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Test
passed #560
ubuntu-16.04

00:07:22

passed #561
ubuntu-17.10

00:07:45

passed #562
ubuntu-18.04

00:07:37