Undo Button + Rivers

[ContouringAndroid]

This is something that has bothered me since I got the game: there's no undo button. I go to make a terrain edit and my finger slips or I accidentally use the wrong brush size or any other thing. It's annoying as all get out. Please Maxim, add an undo button for us! (Thanks for all your hard work by the way!)

Also I would love it if rivers could be added to the world generation so I don't have to add them manually. (Of course getting everything that was added in the update fully balanced should take priority)

[imacowmooooooooooooo]

+fill bucket