Implementing #36
Maya separated from main.py
The menu-item is being added directly within the userSetup.py where it belongs (though using quite the hacky implementation, do have a look to see if you can improve).
Fixes #37 and moves default plugin registration into plugin-module.
select_transform

Including children of transform
validate_mesh_history

Validator to check for mesh construction history, with test example.
Rebased commit from @tokejepsen