Use a macro for form tags

This will stop us repeatedly forgetting to add `novalidate` and
`autocomplete='off'` to our forms (which is how most of them are set
up).

It uses sensible defaults, based on how we most-commonly configure
forms:
- most of our forms are `post`ed (but this can be overridden)
- `autocomplete` should only be enabled where it makes sense, otherwise
  it’s more annoying than useful (but this can be overriden)
- we should never be using HTML5 form validation because our own error
  styles and messages are better

app/templates/views/organisations/organisation/settings/edit-name/confirm.html

@@ -1,6 +1,7 @@
 {% extends "org_template.html" %}
 {% from "components/textbox.html" import textbox %}
 {% from "components/page-footer.html" import page_footer %}
+{% from "components/form.html" import form_wrapper %}
 
 {% block org_page_title %}
   Confirm organisation name change
@@ -13,7 +14,7 @@
   <div class="grid-row">
     <div class="column-three-quarters">
 
-    <form autocomplete="off" method="post">
+    {% call form_wrapper() %}
       {{ textbox(form.password) }}
       <p> Your organisation name will be changed from {{ current_org.name }} to {{ new_name }} </p>
       {{ page_footer(
@@ -21,7 +22,7 @@
         destructive=destructive,
         back_link=url_for('.organisation_settings', org_id=current_org.id)
       ) }}
-    </form>
+    {% endcall %}
     </div>
   </div>
 

app/templates/views/organisations/organisation/settings/edit-name/index.html

@@ -1,6 +1,7 @@
 {% extends "org_template.html" %}
 {% from "components/page-footer.html" import page_footer %}
 {% from "components/textbox.html" import textbox %}
+{% from "components/form.html" import form_wrapper %}
 
 {% block org_page_title %}
   Change organisation name
@@ -9,13 +10,13 @@
 {% block maincolumn_content %}
 
   <h1 class="heading-large">Change organisation name</h1>
-  <form method="post">
+  {% call form_wrapper() %}
     {{textbox(form.name)}}
     {{ page_footer(
       'Save',
       back_link=url_for('.organisation_settings', org_id=current_org.id),
       back_link_text='Back to settings',
     ) }}
-  </form>
+  {% endcall %}
 
 {% endblock %}