Physically-based sizing

Previous attempts at sizing the panel would disregard the actual part people care of: how easy it is to press buttons.

This tries to take it into account as much as possible without altering layouts themselves. As a result, the layout will never be too small if there's enough horizontal space – as long as the size doesn't exceed half vertical space.

As a result, the panel should be sized more appropriately for a wider range of devices.