Show a proper object for the Selection Object
![Screen Shot 2019-03-19 at 4 39 18 PM](https://user-images.githubusercontent.com/4199296/54648988-91d02380-4a65-11e9-9574-4cd4f9a62a51.png)

I have an artboard and some layers. If I select the containing artboard I get a strange object back from `document.selectedLayers`.

```
{ _object: <MSPage: 0x7fd0c4224e10> }
```

I then have to some special wrapping of this `sketch.fromNative(layer._object)` which seems brittle. I was expecting `document.selectedLayers` to return a wrapped layer object. In other words, I thought that `page.layers[0]` should be the equivalent of `layer`