Add label to Collaboration and BBB pages

refs VICE-4738

flag = none

Test plan:
- Navigate to BigBlue button page (need to set)
- Check the add button
- The button label should be Add Conference
- Navigate to collaboration page
- Check the add button
- The button label should be Add Collaboration

Change-Id: I6e9919056159966aef769f8578761944c6ec333d
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/360513
Reviewed-by: Theo Sorriaux <theo.sorriaux@instructure.com>
QA-Review: Dora Csolakov <dora.csolakov@instructure.com>
Tested-by: Service Cloud Jenkins <svc.cloudjenkins@instructure.com>
Product-Review: Tamás Balogh <tamas.balogh@instructure.com>

app/views/collaborations/index.html.erb

@@ -35,7 +35,7 @@ Teachers or students can set up group collaborations."
       <% if can_do(@context, @current_user, :create_collaborations) && !@hide_create_ui %>
         <a role="button" class="Button Button--primary add_collaboration_link" href="#">
           <i class="icon-add" aria-hidden="true"></i>
-          <%= t('links.collaboration', 'Collaboration') %>
+          <%= t('links.add_collaboration', 'Add Collaboration') %>
         </a>
       <% end %>
     </div>

app/views/conferences/index.html.erb

@@ -38,7 +38,7 @@
         <div class="actions_buttons-container">
           <button type="button" id="new-conference" title="Create Conference" class="btn btn-primary new-conference-btn">
             <i class="icon-plus" role="presentation"></i>
-            <%= t(:conference, 'Conference') %>
+            <%= t(:add_conference, 'Add Conference') %>
           </button>
         </div>
       </div>
@@ -47,7 +47,7 @@
         <div class="ic-Action-header__Secondary">
           <button type="button" class="btn btn-primary new-conference-btn" title="<%= t(:new_conference, 'New Conference') %>" aria-label="<%= t(:new_conference, 'New Conference') %>">
             <i class="icon-plus"></i>
-            <%= t(:conference, 'Conference') %>
+            <%= t(:add_conference, 'Add Conference') %>
           </button>
         </div>
       </div>