A visual update

Hi there,

I invested a bit of time to add some quality of live improvements.

Visuals

• The font used for the numbers next to the puzzle has become a bit bolder and the default hint highlighting now inverts the colors instead of making the numbers thinner. Both of those changes should make it easier to make out the numbers in less than ideal circumstances.
• There’s a new default font for the menu which is slightly taller. 

Undo controls

• There’s now an option to toggle undo by (un-)docking the crank.
• You can now use the dpad (left and right) to undo/redo in addition to using the crank.
  

Bug fixes

• Using the crank in the "delete puzzles" screen no longer crashes the game.