[KE] Remove incorrect accessibility attributes from menu
[KE] Remove incorrect accessibility attributes from menu

* Removes incorrect menu/menuitem roles, and haspopup attributes,
  since this is a list of links, not a "menu" in ARIA terms.
* Makes "Research" menu item focussable so that its submenu can be
  revealed with keyboard navigation.
* Gives each submenu a unique ID.

Part of #2491.

mysociety/pombola,mysociety/pombola,mysociety/pombola,mysociety/pombola,mysociety/pombola,mysociety/pombola