fix(webpack): Fix importing CSS with latest webpack

Webpack 4 will drop any unused imports unless they are declared to have side effects. We have to declare css files as having side effects (despite the fact that it should be obvious), or webpack will just drop it.

Fixes #297

package.json

@@ -95,7 +95,9 @@
     "url": "https://github.com/Tripwire/octagon.git"
   },
   "version": "0.0.0-development",
-  "sideEffects": false,
+  "sideEffects": [
+    "*.css"
+  ],
   "lint-staged": {
     "linters": {
       "src/**/*.js": [