Fixed a nasty bug in Box3From.

- The way it was implemented allows to call setSize then setPosition
and have a false size.
- Changed it. There is still problems, since for example calling to and
changing it will not work. A warning tells it in the doc. Some values
are read-only.
- Updated the UIList, UIPanel, and UIAvatars.
- Fixed the offset bug in the UIList.
- Added a filteredSubCount in Avatar and AvatarContainer.