Add WebUI checking to CI

.github/workflows/webui_ci.yaml

@@ -0,0 +1,31 @@
+name: WebUI CI
+
+on: [pull_request, push]
+
+jobs:
+  check_webui:
+    name: Check WebUI
+    runs-on: ubuntu-20.04
+    defaults:
+      run:
+        working-directory: src/webui/www
+
+    steps:
+    - name: checkout repository
+      uses: actions/checkout@v2
+
+    - name: setup nodejs
+      uses: actions/setup-node@v2
+      with:
+        node-version: '14'
+
+    - name: install tools
+      run: npm install
+
+    - name: lint code
+      run: npm run lint
+
+    - name: format code
+      run: |
+        npm run format
+        git diff --exit-code