jQuery.menu.js improvements: "menu bar" support

Improved the format of jquery.menu.js (a long-standing request on my part) to make it easier to understand and make it possible to unit test (unit tests to follow this) by a refactoring.

Additionally added support for "menu bars" which allow us to have sibling menus (like we use in Taxonomy menu on Vistaprint). This allows a way for the menus to know of sibling menus. This allows us to better mimic how native menus behave.