Injects environment variables into the app through webpack, rather than
script snippets in index.html.
As part of this:
* Updated server.js to use node’s path package to resolve file paths
* Ensure that all url environment variables passed to the app don’t
have a trailing slash, allowing for cleaner template urls
**Note**: There are still a number of constants that should be taken
out of the app and put into environment variables.
Notable changes:
* Updated to babel 6
* Updated polyfills to only include core-js/es6 and core-js/stage/4
rather than entire babel/polyfill set
* Dev server with hot reloading replaces server.js in development
* Updated bootstrap loading to be separate from app’s stylesheets
* Cleaned up some of the font dependencies, removing the need for
templating their paths
