Focus Management

Cursive is awesome.

The only thing I'm struggling with, and where I haven't seen much information in the code, is on focus management.

It would be great to have a tutorial or some more docs on how this is supposed to be handled.

For example, I have a "page" that has a hierarachy like this:

```
> CircularFocus
> LinearLayout
> ScrollView
> List
> Text
> Text
> ...
> EditView
```
*Note*: this is simplified, there are a few `BoxView` etc inbetween.

Now what I'd like to do is just use Tab to cycle through the `EditView` and the individual `List` items.

By default, nothing seems to happen. The Edit has focus and I can't switch to anywhere.

So I tried to used a `OnEventView` to call `c.focus_id(ID_OF_LIST_VIEW)`, and would expect the first list item to be selected, but that doesn't seem to work either.

Any help for this specifically, and a general explanation would be much appreciated.