Code review comment for lp:~widelands-dev/widelands/bug-1378801

Thanks, that gave me a baseline to work from.

-1 to adding buttons for the mountain value. In another game, this kind of thing confused the hell out of me, because I never knew which other values would change when I pressed a button. This way, the user knows that the mountains are the first value that gets changed when you change one of the other values. Until you hit 0% / 100% anyway.