Z-Cursor axis labeling wrong for stack with negative scale

[ckohler]

As by commit a32a7bb the z-Cursor displays line cuts through z-stacks with negative axis scale in z-direction, but the axis labeling is still in the wrong order.

[M. Gronle]

fixes issue 12: 2D plot and z-cursor are now working for negative axisScale values

→ <<cset 2fb9c654757c>>