Allow filter links to be used in combination

Means you can see, for example emails that have failed.

Means adding:
- logic to generate links which can have a type parameter, a status
  parameter, or both
- a ‘pill’ UI component for seeing which filters you currently have
  applied
- some logic to change the page title based on which filters you have
  applied

app/templates/components/pill.html

@@ -0,0 +1,16 @@
+{% macro pill(
+  title,
+  items=[],
+  current_value=None
+) %}
+  <nav role='navigation' class='pill' aria-labelledby="pill_{{title}}">
+    <h2 id="pill_{{title}}" class="visuallyhidden">{{title}}</h2>
+    {% for label, option, link in items %}
+      {% if current_value == option %}
+        <span aria-hidden="true">{{ label }}</span>
+      {% else %}
+        <a href="{{ link }}">{{ label }}</a>
+      {% endif %}
+    {% endfor %}
+  </nav>
+{% endmacro %}