xrtGlow: alternative Slicer movement mode
xrtGlow: alternative Slicer movement mode

The Slicer stays in position, instead the rest beamline moves.
SHIFT+CTRL+LeftMouse: in the transverse directions
ALT+CTRL+LeftMouse: in the longitudinal direction
The Slicer center coordinates are now displayed if the 'Show Labels' checkbox is checked.
kklmn/xrt,kklmn/xrt,kklmn/xrt,kklmn/xrt