motioner: Fix wtltest project being unable to compile

The project wtltest in motioner subdirectory has been unable to compile
since source re-organization of Mesh class.
Luckily, we can fix it by adding some entries to the project's list of
source files.  We have to add a #ifdef conditional block to make
Mesh-draw.cpp buildable, though.
Add mirror_copy_tree.py utility script for Metasequoia modeling

The script helps to make symmetric models with complex bones.
Typically, humanoid models tend to have fair number of bones and
nearly symmetric along X axis.