Several fixes around overviews, outlines etc (#825)

* Fix outline for headings that have links

Previously produced blank items because it assumed any link in a heading is an anchor

* Filter unlisted items from overviews

Previously they were filtered only when the card was rendered, so their heading was still shown

* [Overview] Add id to group headings

* Hide headings from empty groups

Should never happen but you never know

* [Overview] Ensure "Other" is always last even when no sorting

docs/_includes/grouped-pages.njk

@@ -3,8 +3,8 @@
 <section id="grid" class="index-grid">
 {% set groupedPages = allPages | groupPages(categories, page) %}
 {% for category, pages in groupedPages -%}
-  {% if groupedPages.meta.groupCount > 1 %}
-  <h2 class="index-category">
+  {% if groupedPages.meta.groupCount > 1 and pages.length > 0 %}
+  <h2 class="index-category" id="{{ category | slugify }}">
     {% if pages.meta.url %}<a href="{{ pages.meta.url }}">{{ pages.meta.title }}</a>
     {% else %}
     {{ pages.meta.title }}

docs/_includes/sidebar-link.njk

@@ -1,4 +1,4 @@
-{% if not (isAlpha and page.data.noAlpha) and not page.data.unlisted -%}
+{% if page | show -%}
 	<li>
 		<a href="{{ page.url }}">{{ page.data.title }}</a>
 		{% if page.data.status == 'experimental' %}<wa-icon name="flask"></wa-icon>{% endif %}