Group pages within their own directory

Add `pages` as it's own content type, and move all page content into
the appropriate directory.

Any references to `layout` in the YAML front matter has also been
removed as it's implied by the content type. Except for `about.md`
which does explicity use a different layout.

source/_pages/talks.html.twig

@@ -0,0 +1,45 @@
+---
+title: Talks
+meta:
+  description: 'Information about previous and upcoming talks that Oliver has presented at conferences and user groups'
+use: [talks]
+talks:
+  - title: 'Drupal and the LDAP module'
+    description: A review and demonstration of some of the recent single sign-on work that I did using Drupal’s LDAP module.
+    events:
+      - event: swdug
+        date: 2013-07-10
+
+  - title: 'About the Drupal Association'
+    description: An impromptu talk about what the Drupal Association is, and what work I’ve been doing since I joined the Association staff.
+    events:
+      - event: swdug
+        date: 2014-08-19
+
+  - title: 'Automated testing with Drupal 8 and PHPUnit'
+    description: A workshop that I gave to teach others about automated testing in Drupal 8.
+    type: Workshop
+    events:
+      - event: drupal_bristol
+        date: 2018-06-27
+---
+{% block content %}
+    {% set talks = getTalks(page.talks|merge(data.talks)) %}
+
+    <header>
+        <p class="lead">
+            After giving my first talk in September 2012, I have now given {{ talks|pastEvents|length }} presentations at various conferences and meetups,
+            on topics including PHP, Drupal, Git, CSS and systems administration.
+        </p>
+    </header>
+
+    <div class="spaced-y-10 mt-6">
+        {% include 'talks/upcoming' with {
+            talks: talks|upcomingTalks,
+        } %}
+
+        {% include 'talks/past' with {
+            talks: talks|pastTalks,
+        } %}
+    </div>
+{% endblock %}