add _menu command support

[ondreian]

_menu is a supar secret in game command like _drag that an FE can use to generate UI menus around a specific exist id= type object, would be nice to support it.

[chriscoyier]

Interesting. Visual output:

>_menu
*******************************************************
*                                                     *
* This is a system command used by the StormFront FE. *
* Attempts to use it improperly will be logged and    *
* investigated.                                       *
*                                                     *
* Verified abuse can result in account suspension.    *
*                                                     *
*******************************************************