WindowServer+Taskbar: Show applets in taskbar :^)

WindowServer now collects applet windows into an "applet area" which is
really just a window that a WM (window management) client can position
via IPC.

This is rather hackish, and I think we should come up with a better
architecture eventually, but this brings back the missing applets since
the global menu where they used to live is gone.

Userland/Services/WindowServer/WindowFrame.cpp

@@ -217,6 +217,8 @@ Gfx::Bitmap* WindowFrame::window_shadow() const
         return s_menu_bar_shadow;
     case WindowType::Taskbar:
         return s_task_bar_shadow;
+    case WindowType::AppletArea:
+        return nullptr;
     default:
         if (auto* highlight_window = WindowManager::the().highlight_window())
             return highlight_window == &m_window ? s_active_window_shadow : s_inactive_window_shadow;