refactor: use Hugo's cascade system for edit, related, breadcrumb

BREAKING CHANGES:

The editable and show_related options must now be controlled from front matter, either directly or cascaded from Hugo config

Move breadcrumb option from params.yaml to front matter `show_breadcrumb: true`

wowchemy/layouts/partials/book_layout.html

@@ -1,8 +1,7 @@
 {{ $current_page := . }}
 
 {{/* Check whether to show breadcrumb navigation. */}}
-{{ $breadcrumb_page_types := site.Params.breadcrumb.page_types | default dict }}
-{{ $show_breadcrumb := index $breadcrumb_page_types .Type | default false }}
+{{ $show_breadcrumb := .Params.show_breadcrumb }}
 
 <div class="container-fluid docs">
   <div class="row flex-xl-nowrap">

wowchemy/layouts/partials/page_edit.html

@@ -1,6 +1,5 @@
-{{/* This makes `edit_page` optional in `params.toml` and prevents errors if it's removed. */}}
-{{ if site.Params.edit_page }}
-{{ if site.Params.edit_page.repo_url | and (index site.Params.edit_page.editable .Type) | and (ne .Params.editable false) | or .Params.editable }}
+{{/* Add link to let visitors edit the page on GitHub. */}}
+{{ if .Params.editable | and site.Params.edit_page.repo_url }}
 {{/* Get language subfolder for multilingual sites. */}}
 {{/* Limitations: the subfolder param, `<LANG>.contentDir`, is unexposed in the Hugo `site` API so we attempt to workaround this issue. */}}
 {{ $content_dir := "content" }}
@@ -16,4 +15,3 @@
   </a>
 </p>
 {{ end }}
-{{ end }}

wowchemy/layouts/partials/page_related.html

@@ -1,6 +1,5 @@
-{{/* This makes `show_related` optional in `params.toml` and prevents errors if it's removed. */}}
-{{ if site.Params.show_related }}
-{{ if (index site.Params.show_related .Type) | and (ne .Params.show_related false) | or .Params.show_related }}
+{{/* Show related/recommended content. */}}
+{{ if .Params.show_related }}
   {{ $related := site.RegularPages.Related . | first 5 }}
   {{ with $related }}
   <div class="article-widget content-widget-hr">
@@ -13,4 +12,3 @@
   </div>
   {{ end }}
 {{ end }}
-{{ end }}