Config params

This PR increases compatibility with the pod organizational structure and sets application parameters via config.

For pods:
* Adding the `app/pods` directory makes it obvious that this structure is supported.
* In `app.js`, setting `podModulePrefix` enables resolving pods.
* In `isolated_container.js` adding `podModulePrefix` enables isolated testing of components using the pod structure.

With this setting, component tests pass if `app/components/pretty-color.js` is moved to `app/pods/pretty-color/component.js`.

My setup for the config files is fairly verbose. I’d welcome any suggestions.

Not sure if this should be separated into 2 specific PRs.

Thanks!