Move the rest of the configuration into template-config.js. This way the options are explicitly in the same namespace so we won't be surprised when we add a variable with the same name as an html-webpack-plugin option.
Rename template extension to ejs for syntax-coloring purposes.
Now that Raven is bundled with webpack, it's not available in the global context, so require it and configure it within the init module.
I struggled to figure out how to expose the raven-js module as a global, as all the combinations of `externals` and `ProvidePlugin` only applied to webpacked modules, not the global window. The correct way to do it seems to be exports-loader but that looked rather hacky and hard to understand.
