Left and main main menu namespace support

Adding support for Namespacing in the LeftAndMain menu. Required replacing backslashes with hyphens in three locations: X-Controller header (when changing admin page), assigning a class to the list item, and in the '$Code' variable sent to the menu (for the id attribute of the list item).

While there is still a lot of work to do in terms of full namespace support on the Frontend side of the CMS, this is a small jump in the right direction.