Make template usage on dashboard easier to scan

The dashboard looked a bit table-y. This commit makes four main changes:

- show a bar chart (drawn in CSS) for template usage (only shown if
  you’ve used more than one template recently)
- only break down template usage by template name, not template type
  (because that’s happening with the big numbers)
- change the style of the ‘show more’ links under each section so that
  they are all consistent, and a little less busy (one less keyline)
- remove the ‘recent templates‘ title so that the first two sections of
  the page group under ‘in the last 7 days’

app/templates/components/show-more.html

@@ -0,0 +1,3 @@
+{% macro show_more(url, label) %}
+  <a href="{{ url }}" class="show-more"><span>{{ label }}</span></a>
+{% endmacro %}