Use the staticfiles app to serve static media in dev

Looks like we [reconfigured apache in vagrant](https://github.com/mozilla/kuma/commit/18028cba8e35e6e514a230d78e0e4262915c32f7) to serve static media after a `collectstatic` command, like prod.

It's more useful to [serve static files using the staticfiles view](https://docs.djangoproject.com/en/dev/ref/contrib/staticfiles/#static-file-development-view) in dev. Otherwise, you have to run `collectstatic` each and every time a static resource is modified.