- Add a parent switch to the main spine control, to allow using the
  key baking operator to convert between moving and fixed root bone.
- Add hips, chest and head as parents for children of the spine.
- Use 'Fix Shear' Inherit Scale and 'Make Uniform' Copy Scale in limbs.
- Switch code to use the new inherit_scale parameter of set_bone_parent.
- Allow local matrices in adjust_widget_transform_mesh.