Fix various team accessibility issues.

Authors:
  - Peter Fogg
  - Daniel Friedman

TNL-1953

lms/templates/components/header/header.underscore

@@ -1,7 +1,7 @@
 <header class="page-header has-secondary">
     <div class="page-header-main">
         <% if (breadcrumbs !== null && breadcrumbs.length > 0) { %>
-            <nav class="breadcrumbs">
+            <nav class="breadcrumbs" aria-label="<%- nav_aria_label %>">
             <% _.each(breadcrumbs, function (breadcrumb) { %>
                 <a class="nav-item" href="<%= breadcrumb.url %>"><%- breadcrumb.title %></a>
                 <span class="icon fa-angle-right" aria-hidden="true"></span>