Normalize and enforce single quotes in styles

- Replace stylelint property in package.json with .stylelintrc.js
- Add string-quotes stylelint rule
- Fix quotes

package.json

@@ -22,34 +22,6 @@
     "android 4",
     "opera 12"
   ],
-  "stylelint": {
-    "extends": "stylelint-config-standard",
-    "rules": {
-      "no-empty-source": null,
-      "at-rule-no-unknown": [
-        true,
-        {
-          "ignoreAtRules": [
-            "extend",
-            "at-root",
-            "debug",
-            "warn",
-            "error",
-            "if",
-            "else",
-            "for",
-            "each",
-            "while",
-            "mixin",
-            "include",
-            "content",
-            "return",
-            "function"
-          ]
-        }
-      ]
-    }
-  },
   "scripts": {
     "build": "webpack --progress --config resources/assets/build/webpack.config.js",
     "build:production": "webpack --progress -p --config resources/assets/build/webpack.config.js",