Prepare for updated Resolver.

* Makes `config/environments.js` into an ERB file.
* Adds a custom method to the Resolver for `resolveSerializer`.
* Uses `typePrefix` to resolve adapters, serializers, and the Router.

There is a PR pending on the resolver repo ([here](https://github.com/stefanpenner/ember-jj-abrams-resolver/pull/16)) to make the behavior in `resolver_ext.js` not needed at all (we can remove it).