quaternion rotations are ignored on iOS/XCode

[kcoley]

Since iOS and XCode currently do not support quaternion xform rotations, add an option to convert quaternion rotations to baked linear Euler rotations:

#50

[kcoley]

I added a new flag called "--use-euler-rotation". Using this should get the rotations to work by converting the rotation quaternions to euler angles. Note that this won't be smooth for all animations.

[wave-electron]

@kcoley I was trying this out today, and basically if you rotate more than 180 degrees in one direction it jumps a little. Is that because of gimbal lock when using euler rotations? i'm assuming quaternion rotations don't suffer the issue.

[kcoley]

@wave-electron yes, I think it is gimbal lock related. I am currently using the USD apis to directly convert the quaternions to euler angles. I'm hoping an iOS update would support quaternions, but in the meantime, I may try to come up with a better algorithm to prevent the jumps.