Menu: Converted mobile panel menu to multiple WAI-ARIA menus

* Switched from a WAI-ARIA tabs to WAI-ARIA menus since it makes more sense through a screen reader
* Split up the the navigation for site menu, secondary menu and site information so they each have their own tab stop and behave like 3 independent menu systems (easier to understand semantically)
* Fixed the default menu opening based upon wb-navcurr

Note: This no longer behaves like an accordion. Multiple menus can be opened at the same time. Is that okay or should any newly opened menu result in the others being closed? @thomasgohard What do you think?