Add @ui interpolation for behavior events

Fixes #1055

This makes `test.events` work. 

```js
V = Marionette.ItemView.extend({
  template: _.template('<div class="doge"></div><div class="coins"></div>'),
  ui: {
    coins: '.coins'
  },
  behaviors: {
    test: {}
  }
});

test = Marionette.Behavior.extend({
  ui: {
    doge: '.doge'
  },

  events: {
    'click @ui.doge': 'onDogeClick',
    'click @ui.coins': 'onCoinsClick'
  },

  onDogeClick: onDogeClickSpy,

  onCoinsClick: onCoinsClickSpy

});
```