Blender Git Loki

Added 'LIBRARY_EDITABLE' flag to bpy.props.*

Rationale: custom props on linked objects are editable through ops and the console but the UI code calls RNA_property_editable() which returns false if (id->lib && !(prop->flag & PROP_LIB_EXCEPTION))

Setting the 'LIBRARY_EDITABLE' flag allows UI templates to change these props (but the changes aren't saved!) for things like indices into CollectionProperties which live on the linked object