Fix HUNs

* Add and prefer a heads up template which is
  the base template + actions
* When a HUN shows a template with a header,
  only allow hiding that header if there is
  no large icon to avoid a visual mess.

Bug: 163626038
Test: manual
Change-Id: Ia42e0a6b1b1ecd4dd438a817f9442a838a2bdb5c