[FR] Buttons: add option to ignore clicks with right mouse button

[basteln]

@yfede

Unfortunately, that suffers of the problem that I have mentioned above: upon right click, the “down” state is painted as if a the mouse action reaches the button, even if a click is not actually triggered.

@yfede I found that the wrong painting can be avoided by overriding mouseEnter, mouseExit, focusGained, focusLost and internalClickCallback as well. I think this puts me firmly in “evil” land, so if anyone has a cleaner way I’d be happy to know
In focusGained and focusLost you don’t get a MouseEvent, but you can check ModifierKeys::getCurrentModifiers().isPopupMenu() instead.