Update built-in cursors. (#246)

- Not all Qt::CursorShapes are supported on all platforoms
   - e.g. on Wayland (Ubuntu 24.04) Qt::SizeAllCursor is not available and
     falls back to its arrow cursor
   - added built-in Crosshair and Move cursors, so that they should be available
     across all platforms
- Redesigned existing object creation cursors
   - Crosshairs are now 3-pixels wide
   - Added white outlines to all cursors to aid in visibility against diverse
     backgrounds

glabels/LabelEditor.cpp

@@ -635,11 +635,11 @@ namespace glabels
 				if ( mModel->isSelectionAtomic() &&
 				     !mModel->handleAt( mScale, xWorld, yWorld ).isNull() )
 				{
-					setCursor( Qt::CrossCursor );
+					setCursor( Cursors::Crosshair() );
 				}
 				else if ( mModel->objectAt( mScale, xWorld, yWorld ) )
 				{
-					setCursor( Qt::SizeAllCursor );
+					setCursor( Cursors::Move() );
 				}
 				else
 				{