Change axis that TKAdjustableNumber is dragged on

I think it'd be more intuitive if you dragged TKAdjustableNumbers up and down, rather than left and right, to change their values. This can be implemented by changing one whole character of code :-) [change 'x' to 'y' in line 220 of TangleKit.js].

Actually, I just noticed that the cursor image when hovering over a TKAdjustableNumber has to be changed as well to match the interaction change.

I notice that sometimes you use horizontal fill bars to show the extent of change that is possible, in which case horizontal dragging is more intuitive, but I think in the default case of just a number and no visual indication of the maximum and minimum values, dragging a number up to increase its value and vice versa makes more sense than dragging it left to decrease and right to increase.