Fixed a bug where notifications could reappear

With sensitive notifications a user could get into
a situation where the groupsummary would not be cleared
because its dismissability was never updated and based
on the visibility of the veto button. This is now corrected.

This Cl also cleans up the veto button handling overall and
ensures that there's no stale state arond it.

Change-Id: Ic7df8d382146d7863ee551c1daa8ba5ed384c7b5
Fixes: 30056258