allow async load?

[dxe4]

if this line is removed
if (!window.OT) throw new Error('You must include the OT library before the OT_Angular library');

and this is removed

  .factory('OT', function() {
    return OT;
  })

and OT injection changes to window.OT

and OT.$.eventing(OTSession);
changes to

      var _interval = $interval(function(){
        if (window.TB) {
                $interval.cancel(_interval);
                OT.$.eventing(OTSession);
        }
      }, 500);

then you can have:

        service.addScript = function(url, defer) {

           if (window.TB) {
                 defer.resolve()
                 return
            }

            var script = document.createElement('script');
            script.type = 'text/javascript';
            script.async = true;
            script.onload = function(){
                defer.resolve();
            };
            script.src = url;
            document.getElementsByTagName('head')[0].appendChild(script);
        }

and in state definition:

resolve : {
    TBloaded: function(){
            service.addScript("...tokboxjslink...", defer)
           return defer.promise
     }
}

so then you can load tokbox asynchronously (and you can also register window.onload event to download tokbox after everything else has loaded). I think it makes a big difference because its a big library.

I could make a pull request but i probably won't find time to unit-test it, but if someone feels like doing it here's the coded needed.