The mouse events/build menu could use some more finetuning

[El-Magico777]

Describe the bug

• moving map around: normally you can click on for example sea and then drag the map around. But if you then pass the PlayerInfoOverlay with the mouse cursor, it keeps dragging even when you no longer have the left mouse button pressed down. You then need to click somewhere again, to stop moving the map.

• clicking to another tab in the Build menu: when you're for example on the Attack tab and have Atom bomb selected. The Atom bomb will stay selected even after you move from the Attack tab to the buildings tab. When you then move the mouse cursor over the map, it still shows a crosshair to send an atom bomb there. While I'd expect Atom bomb (or whatever you had selected on the previous tab) to be unselected once moving over to a different Build menu tab.

[El-Magico777]

fix in pr #30