add new widget ListManager (#1005)

* add new widget ListManager

* flake8 complains

* Null_action appears now in the main list (to simplify additions to the list)
Formatted data are now at the from to the actions submenu

* Define a default action in the menu, potentially independent of a null_action
Both default and null actions don't have to be part of the element's action list
Some cleanup

0 files changed, 0 insertions, 0 deletions