Update Window Size

[TurekBot]

I've been tinkering with the UI customizations that you can make in the manifest. See #158

When I tried to make the update window big, by setting the wrapperStyle to something like -fx-pref-width: 600;, it didn't make the window any bigger.

I think the reason this didn't work is that a window's size doesn't change if the thing it contains gets any bigger.

If we add an updateWindowHeight and updateWindowWidth—or even just an updateWindowSize—is there any easy way to change the size of that update window?

If we're willing to change the UIProvider interface's init method to pass along the manifest as well as the stage, we can have the DefaultUIProvider pluck those size values out of the manifest and change the stage size.

Is there a better way?