Add ui-router to Horizon

Horizon currently uses ngRoute for angularjs routing. This has a limitation that it can only control a single ng-view at a time. It cannot control nested ng-views - that is:

 html <ng-view>
       html <ng-view>
            html

This has become a burdensome restriction on the Swift UI where the design of the code is overly complex because of the lack of nesting. The top view (selected container) and the nested view (selected folder) must know about each other in complex ways in order to keep consistent. A single view might be used that simplified things, but would result in re-loading the container information on every folder path change.

The solution is to switch to ui-router <https://github.com/angular-ui/ui-router>, which is an add-on to angularjs. ui-router operates with two concepts: states and views. States represent a "place" in the application and are positioned in HTML using "<div ui-view></div>" which is filled in with state templates (which will typically have a controller associated with them). Those templates may have "<div ui-view></div>" within them, indicating where child states go with their own template and controller. So for example, in Swift UI, the states could look like:

 $stateProvider
   .state('containers', {
        url: "/containers",
        templateUrl: 'containers.html'
   })
   .state('containers.container', {
        url: "/:container",
        templateUrl: 'container.html'
   })
   .state('containers.container.objects', {
        url: "/*folder",
        templateUrl: 'objects.html'
   });

Concrete steps to take:

0. bundle ui-router as an xstatic package for testing
1. create a Proof Of Concept patch using ui-router
2. assuming #1 is a success migrate Swift UI to use ui-router