searchDisplay, and others: Switch from provider title to provider icon

Display a '+' icon on the provider icon if there are more results that are
hidden. If the provider icon is clicked, ask the provider to launch itself and
perform a search with the current terms.

https://bugzilla.gnome.org/show_bug.cgi?id=681797

js/ui/wanda.js

@@ -136,7 +136,8 @@ const WandaSearchProvider = new Lang.Class({
     Extends: Search.SearchProvider,
 
     _init: function() {
-        this.parent(_("Your favorite Easter Egg"));
+        this.parent();
+        this.id = 'wanda';
     },
 
     getResultMetas: function(fish, callback) {