Make skin pattern layer 0 inherit from skin pattern
Make skin pattern layer 0 inherit from skin pattern

When the user changes the skin pattern, he'd also expect the skin pattern for layer 0 to change. This commit makes the knowledge prerequisite smaller.

Contributes to pull request #1290.

fieldOfView/Cura,ynotstartups/Wanhao,Curahelper/Cura,Curahelper/Cura,hmflash/Cura,fieldOfView/Cura,ynotstartups/Wanhao,hmflash/Cura