search: Make the results take more horizontal space

In order to make gnome-shell search functionality fit on
smaller screens, like those of devices, search results
need to take advantage of more horizontal space so that
any extra space can be used efficiently.

In order to do so, change the layout of the ListSearchResult
class from a vertical one, to a horizontal one and also
decrease the padding of the list-search-result-content css
class.

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