script-parser: Be more strict with "children" members
script-parser: Be more strict with "children" members

The "children" member for Container definitions should only reference
actors, and warn about any other type.

rkudiyarov/clutter_osx,dlespiau/clutter,dlespiau/clutter,djdeath/clutter,djdeath/clutter-multithreaded,ebassi/clutter,djdeath/clutter-android,heysion/clutter-clone,djdeath/clutter,nobled/clutter,collects/clutter,ebassi/clutter,ebassi/clutter,GNOME/clutter,Distrotech/clutter,jigpu/clutter,djdeath/clutter-android,rkudiyarov/clutter_osx,djdeath/clutter-multithreaded,ebassi/clutter,collects/clutter,djdeath/clutter-multithreaded,djdeath/clutter-android,djdeath/clutter,Distrotech/clutter,djdeath/clutter-android,jigpu/clutter,kerrickstaley/clutter-vala,heysion/clutter-clone,dlespiau/clutter,collects/clutter,kerrickstaley/clutter-vala,jigpu/clutter,djdeath/clutter,djdeath/clutter,jigpu/clutter,kerrickstaley/clutter-vala,djdeath/clutter-multithreaded,spatulasnout/clutter,jigpu/clutter,collects/clutter,collects/clutter,GNOME/clutter,spatulasnout/clutter,GNOME/clutter,spatulasnout/clutter,Distrotech/clutter,Distrotech/clutter,rkudiyarov/clutter_osx,kerrickstaley/clutter-vala,ebassi/clutter,spatulasnout/clutter,jigpu/clutter,djdeath/clutter,Distrotech/clutter,heysion/clutter-clone,GNOME/clutter,spatulasnout/clutter,djdeath/clutter-android,nobled/clutter,nobled/clutter,rkudiyarov/clutter_osx,GNOME/clutter,heysion/clutter-clone,Distrotech/clutter,heysion/clutter-clone