Merged requested to merge DEICH-6199-hide-search-all-button into master
An issue was found related to moving back in history: the [Utforsk alle bøker og medier] button did n ot show up. In addition, the button for normal search has disappeared right away before the autocomplete list was displayed.
To overcome these issues the Header component is listening to dropdownShowing callbacks, which originates from the CommandSearch or Autocomplete components.
To guarantee correct functioning of CommandSearch, the component must always be part of the REACT dom, so that it can notify Search->Header as its dropdown is hidden.