Revert "Revert "trying to add first CI and docker image building""

This reverts commit 5b4d74b1

.gitlab-ci.yml

+variables:
+  # all submodules will be cloned recursively upon start of CI job
+  GIT_SUBMODULE_STRATEGY: recursive
+  GIT_SSL_NO_VERIFY: "true"
+
+stages:
+  - build
+
+##########################
+# BUILD stage            #                                
+##########################
+
+build_image:
+  # description: triggers a build of the project as a Docker image,
+  #              each branch will have an individual Docker image that will be used
+  #              in the following stages of the pipeline for testing the code
+  stage: build
+  tags:
+    - docker-image-build
+  script:
+    - ignore

Dockerfile

+# The release set in this Dockerfile defines the release of the whole project
+# and is parsed by every setup script and by the installation instructions.
+# Be aware of this effect if you edit the release here!
+FROM atlas/atlas_external_cvmfs
+ADD . /calypso
+WORKDIR /build
+RUN setupATLAS && \
+    asetup master,latest,Athena && \
+    cmake -DCMAKE_INSTALL_PREFIX=../run ../calypso && \
+    make
+