making menu accessible on mobile when in desktop mode

On screens more narrow than 570px (mainly phones) the min-width and username is removed from the header so the menu can fit. Within topics extra-info-wrapper is hidden (same as mobile layout) so menu can fit.

https://meta.discourse.org/t/once-you-switch-to-desktop-view-on-mobile-there-is-no-way-to-switch-back/18189