virtualdesktops: Fix direction for axis shortcuts
Axis shortcuts currently switch desktops in the opposite direction than when the user switches them by scrolling on the Pager widget, Desktop, etc.
As we can see from Commit 5b3529ac ("Add axis support to zoom effect"), "PointerAxisUp" actually corresponds to scrolling down, and "PointAxisDown" corresponds to scrolling up.
Edited by Yevhen Popok