Added stylelint for pure css

Starting the process of moving away from using pre-processors, so I
added some stylelinting that will keep my pure css tight while still
using prettier for formatting.

.stylelintrc

@@ -0,0 +1,3 @@
+{
+  "extends": "stylelint-config-standard"
+}

package.json

@@ -19,6 +19,8 @@
     "theme_dir": "src/themes/theme-fipamo-default/fipamo-default"
   },
   "devDependencies": {
-    "@parcel/transformer-sass": "^2.2.1"
+    "@parcel/transformer-sass": "^2.2.1",
+    "stylelint": "^14.14.0",
+    "stylelint-config-standard": "^29.0.0"
   }
 }