Blender Git Loki

UI: Support array properties for UILayout.prop_decorator()

Previously `UILayout.prop_decorator()` (or `uiItemDecoratorR()` in C)
only worked for single items, not for arrays. The decorators are added
vertically, like `UILayout.prop()` adds them.
This will be needed for adding decorators to material properties, but
will likely have other use-cases as well.

Also, `None` (or `NULL`) can be passed for the data-pointer and property
now to create blank decorators (as already possible for
`uiItemDecoratorR_prop` in C).