[chore] Adding Stylelint

This is the baseline for Stylelint configuration. No violations exist
with the uncommented rules. The rules that are commented out at the
beginning of the line should be considered for enabling, as well as
fixing them up.

package.json

@@ -62,6 +62,9 @@
     "sinon": "^2.3.2",
     "source-map": "^0.7.3",
     "style-loader": "^0.21.0",
+    "stylelint": "^9.2.1",
+    "stylelint-declaration-use-variable": "^1.6.1",
+    "stylelint-order": "^0.8.1",
     "ts-loader": "^4.4.1",
     "tslint": "^5.10.0",
     "typescript": "^2.9.2",
@@ -84,6 +87,7 @@
     "url": "git+https://github.com/danielyxie/bitburner.git"
   },
   "scripts": {
+    "lint:style": "stylelint ./css/*",
     "start:dev": "webpack-dev-server",
     "build": "webpack --mode production",
     "build:dev": "webpack --mode development",