Use _leftBox as an anchor instead of activities which may not be there

Created by: shemgp

Now I know why I wasn't getting the menus: it's because I hid the "Activities" actor using the Hide Activities extension. Here's a fix that will always add the menus even if the "Activities" is not there. Also, I added a way to wait for idle adding of "applets" before it adds the menu (which I got from Window Buttons extension)

Now my setup looks almost like Unity: