search: Propagate searchResults down the hierarchy

In order to prepare for applying the bold style to the part
of the description that matches the search terms, we need
to listen for the signal that announces the fact that the
search terms have changed. Given the fact that the
SearchResults class is aware of the changes regarding the
search terms, the classes that extent SearchResult need
to have a reference to it in order to listen for the
to-be-implemented 'terms-changed' signal.

https://bugzilla.gnome.org/show_bug.cgi?id=749957