Adding the ability to put (CSS) classes on menu items.

Making use of it by adding a "collapsed" class to the admin menu's settings
top-level item to have it collapse by default (with some adjustment to the admin.js)

work item: 17599

--HG--
branch : 1.x

src/Orchard.Web/Core/Settings/AdminMenu.cs

@@ -21,7 +21,7 @@ namespace Orchard.Core.Settings {
             builder.AddImageSet("settings")
                 .Add(T("Settings"), "99",
                     menu => menu.Add(T("General"), "0", item => item.Action("Index", "Admin", new { area = "Settings", groupInfoId = "Index" })
-                        .Permission(StandardPermissions.SiteOwner)));
+                        .Permission(StandardPermissions.SiteOwner)), new [] {"collapsed"});
 
             var site = _siteService.GetSiteSettings();
             if (site == null)