add stylelint to validation

.stylelintrc.json

@@ -0,0 +1,9 @@
+{
+    "extends": "stylelint-config-standard",
+    "rules": {
+        "comment-empty-line-before": null,
+        "indentation": 4,
+        "no-descending-specificity": null,
+        "selector-list-comma-newline-after": null
+    }
+}

validate_static

@@ -4,6 +4,7 @@ set -o errexit
 shopt -s globstar
 
 jshint --verbose static/**/*.js
+stylelint static/**/*.css
 validatornu --Werror --skip-non-html static
 validatornu --Werror --skip-non-css static
 validatornu --Werror --skip-non-svg --no-langdetect static