Fix setting new events with @ui interpolation.

fixes https://github.com/marionettejs/backbone.marionette/issues/1408
I would try to get it as close to this as possible: (hopefully this will just work)

```js
beforeEach(function () {
  this.ui     = {'foo': '#foo'};
  this.events = {'click @ui.foo': 'bar'};
  this.barStub = this.sinon.stub();

  this.View = Marionette.ItemView.extend({
    ui     : this.ui,
    events : this.events,
    bar    : this.barStub
  });

  this.view = new this.View();
  this.view.delegateEvents();
});

it("the events should be re-normalised", function() {
  expect(this.view.events).to.deep.equal(this.events);
});
```