Modernize the CI setup

.gitlab-ci.yml

 ---
+# Standard test scenarios
+include:
+  - project: 'core/ci-config'
+    ref: master
+    file: 'config/common/master.yml'
+  - project: 'core/ci-config'
+    ref: master
+    file: 'jobs/common/master.yml'
+
 # Install external dependencies
 before_script:
   - duneci-install-module https://gitlab.dune-project.org/fufem/dune-matrix-vector.git