Use Widget child views in Alloy 1.3.0

Thanks for the widget: very useful and well-documented.

Alloy 1.3.0 allows you to [pass child views to a widget](https://jira.appcelerator.org/browse/ALOY-603) using XML markup, e.g:

```XML
<Alloy>
	<Widget id="popover" src="com.skypanther.alloypopover">
		<TableView id="table" />
	</Widget>
</Alloy>
```

This means that with a little addition to your popover widget, it can be a fully-fledged view-controller-style combination and allows most processing of "whatever is in the popover" to be done in the widget controller and then return whatever necessary to the calling controller, which feels more natural for some cases (e.g. avoiding the need for Alloy.Globals).

I've made a few limited updates in this pull request - completely up to you whether you want to use it, as it depends on a more recent version of Alloy than the original widget.

NB apologies for crazy commits: new to this.