Make Part_Measure_Clear_All icon more intuitive

Previously the icon was made up of a tape measure and a pencil. But pencil
icons normally mean editing something. It was not clear that this icon was
meant to delete all the measurements.

This commit replaces the pencil with a red X to make clear it deletes
something. The X was taken because existing delte icons in FreeCAD also
use a red X.
 - https://www.freecadweb.org/wiki/File:Mesh_Remove_Components.svg
 - https://www.freecadweb.org/wiki/File:OpenSCAD_RemoveSubtree.svg
 - https://www.freecadweb.org/wiki/File:Delete.svg