add GitLab CI config

.gitlab-ci.yml

+image: "engel-simulator-builder:latest"
+
+stages:
+  - check
+  - build
+
+check:
+  stage: check
+  script:
+    - rustc --version
+    - cargo --version
+    - cargo fmt -- --check
+  only:
+    - merge_requests
+
+build-dev:
+  stage: build
+  script:
+    - ls -al /usr/local/cargo/bin
+    - wasm-pack build --dev
+  only:
+    - merge_requests
+
+build-release:
+  stage: build
+  script:
+    - wasm-pack build
+    - cd www
+    - npm install
+    - npm run rust-web-modules
+    - npm run build
+  artifacts:
+    paths:
+      - www/dist
+  only:
+    - master