Controllable window check should also check for focus.

[duhrer]

We have an optional check to confirm whether there is a controllable window open on startup. If no controllable window is open, the settings page is opened and receives focus. However, if a controllable page is open but a non-controllable page is focused, the check will fail. This happens to me a lot when working with the "Manage Extensions" page and another controllable test page.

This mainly affects users who switch between the gamepad and something else, but we should add a fix. I can see two options:

1. Focus on the first available controllable window.
2. Open the settings page.

Probably the first is the best option, but it might require renaming or at least adjusting the wording of the associate preference to better describe the behaviour.

[duhrer]

As long as there's a controllable window, we could also address this with #128.