Switch to multi-column-layout if corebird is maximized

[HeikoAdams]

If corebird is running maximized it should display more than one column since this one column looks ugly in maximized window. Alternatively the ability to maximize the window should be disabled.

[IBBoard]

I don't think this is going to happen - see #443.

Disabling maximise would only half work - nothing stops you manually resizing to full screen size, and putting a limit on the width will always be too narrow for someone.