Improve speed of importing rigid bodies

1)  Simple change (a862baa)

Remove local variable 'renameLRBones'.

2) Improve speed of importing rigid bodies (0746c17)

Because the creation of ncc objects are similar,
I found it's faster by duplicating objects instead of creating them individually.

3) Fix bug (f6d442e)

Fix a small bug in my previous commit (0746c17)