Support passing html attributes into MenuItem
pass explorer-menu-url as a data attribute on the explorer menu link, so that we don't have to define it as a global in admin_base.html
Add register_admin_menu_item hook for registering MenuItems globally
Add an is_shown() method to allow globally-registered menu items to specify whether or not they should be shown on a given request
Convert all remaining menu items to be globally-registered with an is_shown method
Allow menu items to define their own javascript includes, and put the explorer menu js there rather than in core.js
documentation for register_admin_menu_item
Replace the MenuItem.render_js mechanism with the 'media' mechanism from django.forms, which does basically the same thing but better (e.g. handles de-duping where multiple items import the same js file)
add test for MenuItem media being included
Test the register_admin_menu_item hook, including the use of classnames/attrs and is_shown
Merge pull request #535 from gasman/feature/menu-api

Refactor admin menu API to allow menu items to have bundled JS