On mobile, site and subject navs should be collapsable menus

[briandominick]

The mobile version has 2 obvious problems: a margin along the right side and menus that are way too big at the top.

The menus should be collapsed to a hamburger button so the reader sees some content before scrolling.

[briandominick]

On second thought, maybe the initial behavior is just to collapse the subject menus by default on mobile.

Some of that margin can be removed, and maybe just the site nav goes into a hamburger button?

Also here's how that is done in Bootstrap 4.

(Also that weird margin has disappeared wuh?)

[briandominick]

And maybe the breadcrumbs should go above the collapsed subject menus.