Fix 228 - Use bower to fetch app externals

Fixes #228
I was thinking of something like this: In the code calling the template, add a `path` property, with the value depending on the `production` flag: `production ? "/resources" : "/app".

Then use that to create the actual paths:

```html
<link rel="stylesheet" href="{{path}}/download.css">
```

That would work whenever `app/` is replaced with `resources/`.

I'm wondering if the flag is really necessary - maybe its better to remove the flag and force a rebuild of the resources to test changes? `time grunt build-app` takes barely more than two seconds, along with a watch task that's fast enough to not require a separate non-production mode.