add CI

.gitlab-ci.yml

+stages:
+    - build
+  
+build_and_test:
+    image: registry.gitlab.com/rboman_docker/gmsh_python
+    stage: build
+    script:
+        - cd cxxfem
+        - mkdir build
+        - cd build
+        - cmake -DFEM_USE_MKL=OFF ..
+        - make -j 4