[gltf] Support camera and fix hierarchy#772

Merged

cart merged 4 commits intobevyengine:masterfrom FuriouZz:feature/gltf-camera

Nov 7, 2020

+78-33

Commits on Nov 3, 2020

[gltf] Support camera and fix hierarchy
FuriouZz
committed

Commits on Nov 5, 2020

Commits on Nov 6, 2020

[gltf] prefer .with method for component addition
FuriouZz
committed