Sensible window sizes / Zoom button behaviour

[humdingerb]

It'd be nice if the windows showed as many items as possible, while also respecting the last window size.

So, by default open windows with the same size/coordinates as when last closed. If there are more items than fit, extend the window height downwards until you hit the screen border (see MoveOnScreen()). Maybe also extend upwards in that case. Things will get complex...

The Zoom button should also do the sensible thing instead of just maximizing the window.