Option to choose scale at export

[madjin]

currently when exporting VRM without atlas for artists to tune up, the scale shrinks to 0.7 of what most are working with in anata project. This looks fine when fully assembled, but if we need to tune something up it would be better to keep consistent with rest of the project files.

we can use an outline of a default VRM armature from blender as the reference point, then a slider / scale (like how we do 0.7 currently).

I don't think this is a big priority right now, because if we drag and drop a VRM trait into character studio it will scale to appropriate size. I just want to post this just in case.