Made hot collections umd-y

`var el = opts.el || document.createElement('div');`

1) That way you're not adding properties to the opts object you're passed, since it could cause havoc for the person who passed you that object (maybe they then use it for other stuff).
2) We've never defaulted to appending it to the dom for you, just for creating a thisView.el. So the use case I want to work is
```javascript
var myHots = new HotCollectionsApp({ network: 'mine' });
document.body.appendChild(myHots.el);
```