[request] standard\Menubar needs remove button

[reaby]

as mlepp project goes further and plugins can now be more or less be also unloaded from manialive...

Case:
unload MLEPP\admin --> load MLEPP\Admin
unload MLEPP\admin --> load MLEPP\Admin
unload MLEPP\admin --> load MLEPP\Admin
unload MLEPP\admin --> load MLEPP\Admin

Result:
Gazillion of admin entries at menubar

Request:
Expose a public function to also remove buttons from menubar