cursor-shape: Add the 'all-resize' cursor shape

The move cursor is ambiguous, since it is used in two context:
for DND, and for resizing. This commit adds a separate enum
value for a cursor that indicates something can be resized
in all directions. A suitable image for this value is a four-headed
arrow.

Signed-off-by: Matthias Clasen <mclasen@redhat.com>