Mobile menus

Mobile friendly navigation, mostly targeted at students. `menu.js` was recycled for the new navigation, as the old code seems to be unused.
I'm going to leave it in for now. There _might_ be an issue with the user being able to "scroll" (more like pan) the content back over the sidebar instead of just being able to scroll the sidebar up and down, but I'm not sure since I haven't actually tested it on real touch screens yet.