Add autocomplete attribute to password fields

This helps the browser autocomplete them with the right thing.

Value based on https://www.w3.org/TR/WCAG21/#input-purposes

app/templates/views/user-profile/authenticate.html

@@ -19,7 +19,7 @@
     <div class="column-three-quarters">
 
     {% call form_wrapper(autocomplete=True) %}
-      {{ textbox(form.password) }}
+      {{ textbox(form.password, autocomplete='current-password') }}
       {{ page_footer('Confirm') }}
     {% endcall %}
     </div>