Implement Orchid menu functionality and/or assign active class and ARIA to current page

[erinchambers]

This is a "should"—not a "must"—re: WCAG 2.1

From Deque's summary of navigation accessibility:
• A navigation list SHOULD include a visible method of informing users which page within the navigation list is the currently active/visible page. • A navigation list SHOULD include a method of informing blind users which page within the navigation list is the currently active/visible page.

We implemented this in Orchid by adding two things to the current page's navbar link:

1. Add class="active" to the list item (<li>)
2. Add aria-current="page" to the link

...however, the code we used for Orchid doesn't work for Austen Said. Looks like there's already some code in application.html.erb that's trying to add aria-current, but it's not working.

For reference, see the Chesnutt dev site and the corresponding navbar partial.