[IMP] hr_holidays: Added a toogle button widget for report buttons in li...

...stview of 'Employees Leaves' which are making the listview ugly.

Changes the default to TODO.
Fixed the editable list view issue if it is in editable mode and the user clicks on button widget it shows an error 'Cannot read property '$el' of undefined'.

- Task: https://www.odoo.com/web#id=9419&view_type=form&model=project.task&action=333&active_id=131
- Pad: https://pad.odoo.com/p/r.GW8mpTLz1ziIQhrs
an help string "To do" that repeats the filter title "To do" is not useful