Update h1 on pill pages to work with new pill

Pill pages are:
- /notifications
- /template-usage
- /monthly
- /organisations/<organisation_id>
- /templates

Includes changes to:
- the folder-path component
- the page-header component

...all their h1s have the same id.

app/templates/views/organisations/organisation/index.html

@@ -1,3 +1,4 @@
+{% from "components/page-header.html" import page_header %}
 {% from "components/big-number.html" import big_number %}
 {% from "components/live-search.html" import live_search %}
 {% from "components/message-count-label.html" import message_count_label %}
@@ -10,9 +11,7 @@
 
 {% block maincolumn_content %}
 
-  <h1 class="heading-medium">
-    Usage
-  </h1>
+  {{ page_header('Usage', size='medium') }}
 
   <div class="bottom-gutter">
     {{ pill(years, selected_year, big_number_args={'smallest': True}) }}