Add Sass loader, override bootstrap colors

- Changed our main.css to main.scss
- Installed bootstrap locally so we can tweak it
- Installed sass-loader and node-sass
- Updated webpack.config file to include a .scss rule

package.json

@@ -11,7 +11,10 @@
   "author": "",
   "license": "ISC",
   "devDependencies": {
+    "bootstrap": "^4.3.1",
     "css-loader": "^2.1.0",
+    "node-sass": "^4.11.0",
+    "sass-loader": "^7.1.0",
     "style-loader": "^0.23.1",
     "webpack": "^4.29.6",
     "webpack-cli": "^3.2.3"