Do not hard-code nuxeo-search-form in selector to display search result

One may have many different searches and can't afford to add a new drawer menu item for each one and prefer to keep a single search menu where the user can choose the search (through a selector) which updates the search form accordingly.

The issue is that we have selector nuxeo-search-form hardcoded in nuxeo-app and it prevents to leverage a custom xxxx-search-form.