view-selector: filter out disabled search providers

If the added search provider has an appId in the list of the disabled
search providers settings, ignore it.

https://bugzilla.gnome.org/show_bug.cgi?id=687491

js/ui/search.js

@@ -10,6 +10,8 @@ const Util = imports.misc.util;
 const FileUtils = imports.misc.fileUtils;
 const Main = imports.ui.main;
 
+const SEARCH_PROVIDERS_SCHEMA = 'org.gnome.desktop.search-providers';
+
 // Not currently referenced by the search API, but
 // this enumeration can be useful for provider
 // implementations.