sunsky presets

* Mountain: low turbidity, well-defined sun, blue-ish (high sun energy)
* Desert: high turbidity (dust), big, diluted sun, red-ish
* Classic: average turbidity (water vapor), small, diluted sun.

also fixed a bug with saving string presets

release/scripts/ui/properties_material.py

@@ -274,7 +274,7 @@ class MATERIAL_PT_options(MaterialButtonsPanel):
         col = split.column()
         col.prop(mat, "traceable")
         col.prop(mat, "full_oversampling")
-        col.prop(mat, "sky")
+        col.prop(mat, "use_sky")
         col.prop(mat, "exclude_mist")
         col.prop(mat, "invert_z")
         sub = col.row()