Lint LESS files using Stylelint (#1948)

js/.prettierrc.js

@@ -0,0 +1,11 @@
+module.exports = {
+    tabWidth: 4,
+    overrides: [
+        {
+            files: ['*.less'],
+            options: {
+                parser: 'less',
+            },
+        },
+    ],
+};

js/.stylelintrc.js

@@ -0,0 +1,23 @@
+module.exports = {
+    extends: [
+        'stylelint-config-standard',
+    ],
+    customSyntax: 'postcss-less',
+    rules: {
+        'at-rule-empty-line-before': null,
+        'at-rule-name-case': null,
+        'color-function-notation': 'legacy',
+        'color-hex-case': 'lower',
+        indentation: 4,
+        linebreaks: 'unix',
+        'max-line-length': null,
+        'no-descending-specificity': null,
+        'rule-empty-line-before': null,
+        'string-quotes': 'double',
+
+        // TODO
+        'no-duplicate-selectors': null, // 3 errors
+        'selector-class-pattern': null, // 14 errors, example: Expected class selector ".atk-topMenu" to be kebab-case
+    },
+    reportNeedlessDisables: true,
+};