Only call update_style when styles changed and then redraw

* PERFORMANCE!
* fixes #654
* renamed change_style --> update_style (seemed like a better fit)
* do not redraw if the value is just queried and do not update if
  the values of the hash don't change
* maybe update the expert-game-of-life-adjusted.rb now?

Would be happy of a quick review of this so it can go in as fast as possible! =)

Happy pre Easter everyone!
Tobi