Allow ajaxified logics on new elements inside javascript list widget

Use case:

• define a javascript list widget
• include a subwidget handling re-render, like a checkbox showing/hiding an additional field (see checkbox rerender example on https://doc.nuxeo.com/x/Phw5AQ)

=> ajaxified logics will behave properly on existing items, but not on any new item.

This is linked to the fact that server-side component state is not yet aware of newly added components.
Also, selection actions methods should be refined to perform tree traversal without using the absolute component id, since it does not behave properly inside javascript lists.