MDL-56690 theme_boost: Allow menus to scroll in the header
MDL-56690 theme_boost: Allow menus to scroll in the header

The header is fixed - so if menus in the header are longer than the page, you can't scroll
to the bottom of the menu. This sets max height on the menus to the viewport height - the navbar height and sets them to scroll
auto.

dilawar/moodle