Add html-loader, file-loader, and clean-webpack-plugin

- Added html-loader to automatically require the files we reference in img tags
- Added file-loader to handle the svg,png,jpg,gif files from our images
- Configured file-loader to add our images to an imgs directory in dist
- Also configured it to add a hash to their filenames
- Lastly, added clean-webpack-plugin to our production config to clean out the dist directory each time we build

webpack.prod.js

@@ -1,11 +1,13 @@
 const path = require("path");
 const common = require("./webpack.common");
 const merge = require("webpack-merge");
+const CleanWebpackPlugin = require("clean-webpack-plugin");
 
 module.exports = merge(common, {
   mode: "production",
   output: {
     filename: "main.[contentHash].js",
     path: path.resolve(__dirname, "dist")
-  }
+  },
+  plugins: [new CleanWebpackPlugin()]
 });