search-display: Move SearchResults to a separate file

With the new layout, search results will be displayed in an independent
view like window previews, applications and possible future additions;
it does not make much sense keeping it with the switching logic, so move
the code to its own file.

Also remove the dash-prefix from the relevant style classes.

https://bugzilla.gnome.org/show_bug.cgi?id=634948

js/ui/search.js

@@ -182,7 +182,7 @@ SearchProvider.prototype = {
      * implementation will show the icon next to the name.
      *
      * The actor should be an instance of St.Widget, with the style class
-     * 'dash-search-result-content'.
+     * 'search-result-content'.
      */
     createResultActor: function(resultMeta, terms) {
         return null;