Reenable View.attributes from Backbone

Backbone allowed the user to specify View.attributes either as an object or as a method that returns a object. These attributes then get set on the view element (just like the attributes from getAttributes in Rendr). This is functionality that got lost in Rendr and that want to reimplement to remove workarounds like:

```javascript
var View = BaseView.extend({
    getAttributes: function () {
        return _.extend(BaseView.prototype.getAttributes.apply(this, arguments), this.attributes);
    }
});
```