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/dashboard/monthly.html

@@ -1,3 +1,4 @@
+{% from "components/page-header.html" import page_header %}
 {% from "components/big-number.html" import big_number_with_status, big_number %}
 {% from "components/pill.html" import pill %}
 {% from "components/table.html" import list_table, field, hidden_field_heading, right_aligned_field_heading, row_heading %}
@@ -12,9 +13,7 @@
 
 {% block maincolumn_content %}
 
-  <h1 class="heading-large">
-    Messages sent
-  </h1>
+  {{ page_header('Messages sent') }}
   <div class="bottom-gutter">
     {{ pill(
       items=years,