Support dot notation in nested routes

When a route is nested, you can override the
default naming conventions by supplying a handler
name with a dot:

```js
App.Router.match('/customers', function(match) {
  match('/customer').to('customers.show');
});
```

This would look for `App.CustomersShowRoute`,
`App.CustomersShowController`, and the
`customers/show` template.

HAT TIP TO @dgeb