Set forward vector

[Wahooney]

Being able to select the forward vector (without adding rotation to the matrices), would be helpful for engines that have unconventional forward vectors (ie. UE4s X-forward)

Thanks.

[julienduroure]

This is against glTF 2.0 specification:

glTF uses a right-handed coordinate system, that is, the cross product of +X and +Y yields +Z. glTF defines +Y as up. The front of a glTF asset faces +Z.