UI: new icon set by Andrzej Ambroz.

This is a monochrome icon set, with a more modern look and icons for
various features that did not have a proper icon before.

intern/cycles/blender/addon/ui.py

@@ -964,8 +964,8 @@ class CYCLES_PT_context_material(CyclesButtonsPanel, Panel):
             row.template_list("MATERIAL_UL_matslots", "", ob, "material_slots", ob, "active_material_index", rows=rows)
 
             col = row.column(align=True)
-            col.operator("object.material_slot_add", icon='ZOOMIN', text="")
-            col.operator("object.material_slot_remove", icon='ZOOMOUT', text="")
+            col.operator("object.material_slot_add", icon='ADD', text="")
+            col.operator("object.material_slot_remove", icon='REMOVE', text="")
 
             col.menu("MATERIAL_MT_specials", icon='DOWNARROW_HLT', text="")