Add Babel to Auto-Build

[alancleary]

Changes to files in the client are automatically detected, causing the build command to be rerun, which does things such as compile TypeScript files into JavaScript. Babel is currently not part of the build command, so although changes to the JavaScript files in the assets directory are detected, the files are not automatically transpiled and minified. This means the application is reloaded after changes occur, but the changes don't actually affect the application until the developer manually transpiles with Babel. Add Babel to the build command so this manual workflow is automated.

[alancleary]

In commit 595ef69 the build process was moved to webpack. This deprecated our use of babel, leading to its removal in commit eb00650. Fortunately, the files that were previously being manually built with babel are now automatically built with webpack.