Rationalise behaviours of context, container and cover:

- Set minimum dimensions to avoid having to pass classes all over the place.
- Outline the container to show white on white covers properly.
- Remove extraneous code.
- Better size caption when no cover is available.
- Create Alignments, Positions and Spacings sections and move some existing dimensions.
- Update previous templates.

bookwyrm/templates/lists/list_items.html

@@ -14,7 +14,7 @@
                     <div class="card-image columns is-mobile is-gapless is-clipped">
                         {% for book in list_books %}
                             <a class="column is-narrow" href="{{ book.book.local_path }}">
-                                {% include 'snippets/book_cover.html' with book=book.book cover_class='has-height is-h-small' aria='show' %}
+                                {% include 'snippets/book_cover.html' with book=book.book cover_class='is-min-w-none is-h-small' aria='show' %}
                             </a>
                         {% endfor %}
                     </div>