Allow configuration of layerIndex via router DSL

[lukemelia]

Also allow specifying a base class for the route instance.

It would be nice to have this flexibility via Ember's router DSL, but I don't think that is possible today. Instead, we could have our own code that consumes the same function passed to Router.map. It might look like this:

let dsl = function() {
  this.route('yapp', { path: '/yapp/', resetNamespace: true }, function() {
    this.route('page', { path: '/pages/:page_id', resetNamespace: true }, function() {
      this.route('schedule-item', { path: '/schedule-items/:schedule_item_id', resetNamespace: true }, function() {
        this.route('person', { openInNewLayer: true });
      });
      this.route('track', { path: '/tracks/:track_id', resetNamespace: true }, function() {
        this.route('schedule-item', { path: '/schedule-items/:schedule_item_id' }, function() {
          this.route('person', { openInNewLayer: true, routeClass: 'schedule-item.person' });
        });
      });
    });
  });
};

Router.map(dsl);
NavStack.process(dsl);