Fix duplicated chilren in Scene spawn#904

Merged

cart merged 4 commits intobevyengine:masterfrom lassade:fix_dup_children

Nov 22, 2020

+42-24

Commits on Nov 22, 2020

fixed dup children

lassade
authored and
cart
committed
fix children already added (best short term)

lassade
authored and
cart
committed
reorder impls

lassade
authored and
cart
committed
add swap method and update comments
cart
committed