updates to tests for changes to mobile interface

Updated mobile_add_action.feature with new navigation text
  Updated modile_edit_a_todo.feature to not look for removed 'done' checkbox in
  the edit form, but to use the previously created "mark complete" button.
  Added completed_container to mobile_actions so the test could find the
  completed todo that is no longer not visible

app/views/todos/_mobile_actions.rhtml

@@ -4,8 +4,10 @@
 <%= render :partial => "contexts/mobile_context", :collection => @contexts_to_show -%>
 <% end -%>
 <% unless @done.nil? -%>
+<div id="completed_container">
 <h2><%= t('todos.completed_actions') %></h2>
 <ul class="c">
 <%= render :partial => "todos/mobile_todo", :collection => @done %>
 </ul>
+</div>
 <% end %>