Add 'name' key to Body.userData

The format is 'class_name.body_name'.
example (in class Hoge):
    head.userData['name'] = 'hoge.head'
Improve Monitor much

- Show Body's HPs as bars with the body's names.
- Don't show the position.
- Accept offset, size and colors on init.
- Refer to Body.userData['name'].
- Commit suicide when the monitored body die.