Make the dropdown menus keyboard accessible

The newer version of Angular UI bootstrap has
an optional keyboard-nav directive to
make dropdowns keyboard accessible.

Card 89

h/templates/client/group_list.html

-<div class="pull-right" dropdown>
+<div class="pull-right" dropdown keyboard-nav>
   <span class="dropdown-toggle"
         dropdown-toggle
         data-toggle="dropdown"

h/templates/client/publish_annotation_btn.html

-<div dropdown="" class="publish-annotation-btn__btn" is-open="vm.showDropdown">
+<div dropdown="" class="publish-annotation-btn__btn" is-open="vm.showDropdown" keyboard-nav>
   <dropdown-menu-btn
     label="'Post to ' + vm.publishDestination"
     ng-click="vm.save()"

h/templates/client/viewer.html

@@ -18,7 +18,7 @@
                     'other': 'Showing {} selected annotations.'}"></span>
       <a href="" ng-click="clearSelection()">Clear selection</a>.</li>
   <li ng-show="isStream">
-    <span class="ng-cloak" dropdown>
+    <span class="ng-cloak" dropdown keyboard-nav>
       <span role="button"
             data-toggle="dropdown"
             dropdown-toggle>