Apply transforms on export

[buu342]

Add a checkbox for applying all transforms on export (on by default). This should mitigate a really common beginner mistake of moving stuff in object mode.

Animations should have their keyframe indices marked, then the animation must be baked, and only marked indices should be exported. This will prevent that annoying bug where scaled armatures don't scale rotations as well.

[buu342]

This is actually a pain to do, and most plugins (including official ones) don't bother or warn it's problematic with animations. What we should do is get the object's world matrix and scale all vertices by it. Said matrix also includes scaling and stuff from the parent.

[buu342]

Turns out that this is still a pain to do with animations :))))))

[buu342]

In the meantime, I added a warning in fc47441 for when the user attempts to export a model with unapplied transforms.