[REF] web: also use _confirmSave when a kanban record is 'manually' updated

Normal flow for one record's changes to be saved is:

0) (use `_setValue` for fields)
1) `trigger_up('field_changed')`
2) field manager mixin: `_onFieldChanged`
3) model: apply changes and save
4) controller: `_confirmSave`

Kanban records are using another system for an unknown reason. This
system was calling the right model functions but was not calling the
controller `_confirmSave` and was instead re-coding it. This commit
makes sure that `_confirmSave` is now called.