Menu - Adds support for Experimental UI section which includes the new navigation structure in it's current state.

This commit does not reflect the final state of the menu, as there
are current and potential future usability issues to address. What's
included:
 - ability to turn experimental UI on and off per user
 - new navigation structure in experimental mode
 - modified navigation rendering for experimentation
 - tests for new navigation rendering
Menu - Converts to a structure of items and menus with base classes that define each.  All clickable links are items while collections of items and menus are menus.
Experimental Menu - Removes the need for a file to instantiate menus and moves the prune into the menu class itself. Includes updates to tests and menus to account for this new structure.