Fix for #723.  Use express body parser only when not proxying.

My previous [commit](https://github.com/stefanpenner/ember-cli/commit/cfaa0c5b560c4526a86e0e62166d999dfc67598c) made killed the ability to make ```POST``` requests when using the API server as a proxy.  See https://github.com/stefanpenner/ember-cli/issues/723.

This put the body-parser behind the scenes with the other parts of ```emberCLIMiddleware```, and it would only add the body parser if it wasn't using the proxy.

For whatever reason, ```body-parser``` doesn't work when included after the routes declaration.  I'm not entirely sure why, but putting it before seems to rectify this.  

Everything seems to work now, but I'm not 100% confident that it's the correct approach.