[Course Navigation] Add a footer at the bottom of the navigation

[Mikee]

Problem statement:

When navigating the vertical menus, there is no indication of the end of a listing. This means new users to the platform don't easily understand that the navigation ends at that point. In some browsers, the bottom option is sometimes obscured if hovering over a link, and in non-production interfaces, the navigation items are not available to click until the notice is removed.

Proposed solution:

Add an icon, line, or indication that the navigation area has no more items that takes up more height than the non-production interface warning banner. (1.5 icon heights, or link heights?)

User role(s):

admin,instructor,student,ta,designer,observer

[Mikee]