With the new views, we lost a (almost unused and undocumented) feature:
the ability to instantiate custom widgets in a form view, not linked to
a particular field. For example:
<widget type="weekly_timesheet" attrs="{'readonly': [['state', 'not in', ['new', 'draft']]]}"/>
We reintroduce this feature in this commit, with a nice twist: it also
works for the list view and the kanban view.