470 External Nav

This brings in the initial work to have rxApp pull menu data from an external source.
Knowing what I know now about how our environments work, I think this will result in it *always* ending up with staging. Once #549 goes in, I'm going to change this to be:

```
var url = routesCdnPath.production;
if (!Environment.isUnifiedProd()) {
    url = routesCdnPath.staging;
}
```