Edit mobile page allows users to proceed without changing mobile number

Also:
- change formatting of mobile number redact characters

- redirect if session empty

- update a test with new mock after rebase

app/templates/views/manage-users/edit-user-mobile.html

@@ -13,7 +13,7 @@
   <p id="user_name">This will change the mobile number for {{ user.name }}.</p>
   <div class="grid-row">
     <div class="column-three-quarters">
-      {% call form_wrapper() %}
+      {% call form_wrapper(class="extra-tracking") %}
         {{ textbox(form.mobile_number) }}
         {{ page_footer(
           'Save',