Allow non-gov email addresses to be changed to gov email addresses

When a user's email address is updated, we not allowing it to be changed
to a non-government email address. We now allow a non-gov email address
to be changed to another non-gov email address. Government email
addresses still cannot be changed to non-government email addresses.

Also fixes the link in the error message on the ChangeEmailAddress form -
this was being escaped before.

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

@@ -14,7 +14,7 @@
   <div class="grid-row">
     <div class="column-three-quarters">
       {% call form_wrapper() %}
-        {{ textbox(form.email_address) }}
+        {{ textbox(form.email_address, safe_error_message=True) }}
         {{ page_footer(
           'Save',
           back_link=url_for('.edit_user_permissions', service_id=service_id, user_id=user.id),