Workbox service worker (#4169)

* Add workbox service worker functionality

* Remove debug

* Set workboxConfig for when there isn't a cra config file

* Remove workbox configuration options as c-r-a isn't planning on supporting optional configuration

* Remove c-r-a config path from paths

* Add workbox service worker functionality

* Remove c-r-a config path from paths

* Inline the webpack workbox config

* Use settings reccommended by @jeffposnick

https://github.com/facebook/create-react-app/pull/4169/#issuecomment-422963072

* Fallback to public url index.html, not root

* Add one comment

* Update comment

* Correct regex

packages/react-scripts/package.json

@@ -59,13 +59,13 @@
     "resolve": "1.8.1",
     "sass-loader": "7.1.0",
     "style-loader": "0.23.0",
-    "sw-precache-webpack-plugin": "0.11.5",
     "terser-webpack-plugin": "1.1.0",
     "thread-loader": "1.2.0",
     "url-loader": "1.1.1",
     "webpack": "4.19.1",
     "webpack-dev-server": "3.1.9",
-    "webpack-manifest-plugin": "2.0.4"
+    "webpack-manifest-plugin": "2.0.4",
+    "workbox-webpack-plugin": "3.6.1"
   },
   "devDependencies": {
     "react": "^16.3.2",