Reduce duplicated code and automate more things

Also change styling for article captions (author/when published)

_includes/image.html

@@ -0,0 +1,4 @@
+<figure>
+    <img src="/images/{{ page.url | relative_url | remove: '.html' | replace: '/', '-' | remove: '-articles-' }}--extra-{{ include.id }}.jpg" style="width:100%;">
+    <figcaption class="mdc-typography--caption-text">{{ include.caption }} &bull; &copy; {{ include.copyright }}</figcaption>
+</figure>