[FIX] Menu widget does not reflow at its startup anymore, usermenu reflows it after being fully initialized
[IMP] Moved load_menus method on the ir.ui.menu model; all topmenu items links redirect to /web; added a is_user method on website and added the menu_data needed to render the topmenu in qwebcontext if the request uid is in user groups; included the backend menu in website.layout